From ed3f21737413d5929feb6a8a6631177963aa28a1 Mon Sep 17 00:00:00 2001
From: Closure Team <closure-library-bot@google.com>
Date: Mon, 4 Oct 2021 15:24:51 -0700
Subject: [PATCH] Adds Intl native ECMAScript support for Closure
 DateTimeFormat. RELNOTES: Add Intl native support in DateTimeFormat.

PiperOrigin-RevId: 400828431
Change-Id: I6e0679b14ff4d7496738b04915f7c10bf50b9367
---
 closure/goog/i18n/BUILD                  |   11 +
 closure/goog/i18n/datetimeformat.js      |  403 ++++-
 closure/goog/i18n/datetimeformat_test.js | 1948 +++++++++++++++-------
 closure/goog/i18n/localefeature.js       |    9 +
 closure/goog/i18n/nativelocaledigits.js  |   40 +
 closure/goog/i18n/numberformat.js        |   47 +-
 6 files changed, 1749 insertions(+), 709 deletions(-)
 create mode 100644 closure/goog/i18n/nativelocaledigits.js

diff --git a/closure/goog/i18n/BUILD b/closure/goog/i18n/BUILD
index 6af94dd0f6..93fee49d2b 100644
--- a/closure/goog/i18n/BUILD
+++ b/closure/goog/i18n/BUILD
@@ -102,10 +102,15 @@ closure_js_library(
     name = "datetimeformat",
     srcs = ["datetimeformat.js"],
     deps = [
+        ":datetimepatterns",
         ":datetimesymbols",
+        ":localefeature",
+        ":nativelocaledigits",
         ":timezone",
         "//closure/goog/asserts",
         "//closure/goog/date",
+        "//closure/goog/date:utcdatetime",
+        "//closure/goog/labs/useragent:browser",
         "//closure/goog/string",
     ],
 )
@@ -187,6 +192,11 @@ closure_js_library(
     ],
 )
 
+closure_js_library(
+    name = "nativelocaledigits",
+    srcs = ["nativelocaledigits.js"],
+)
+
 closure_js_library(
     name = "numberformat",
     srcs = ["numberformat.js"],
@@ -194,6 +204,7 @@ closure_js_library(
         ":compactnumberformatsymbols",
         ":currency",
         ":localefeature",
+        ":nativelocaledigits",
         ":numberformatsymbols",
         "//closure/goog/asserts",
         "//closure/goog/math",
diff --git a/closure/goog/i18n/datetimeformat.js b/closure/goog/i18n/datetimeformat.js
index c6035a4ef4..6de01061e0 100644
--- a/closure/goog/i18n/datetimeformat.js
+++ b/closure/goog/i18n/datetimeformat.js
@@ -14,18 +14,55 @@
  */
 goog.provide('goog.i18n.DateTimeFormat');
 goog.provide('goog.i18n.DateTimeFormat.Format');
-
 goog.require('goog.asserts');
 goog.require('goog.date');
+goog.require('goog.date.UtcDateTime');
+
 goog.require('goog.i18n.DateTimeSymbols');
+
+goog.require('goog.i18n.LocaleFeature');
+goog.require('goog.i18n.NativeLocaleDigits');
 goog.require('goog.i18n.TimeZone');
 goog.require('goog.string');
 goog.requireType('goog.i18n.DateTimeSymbolsType');
 
+goog.scope(function() {
+// For referencing modules
+const LocaleFeature = goog.module.get('goog.i18n.LocaleFeature');
+const NativeLocaleDigits = goog.module.get('goog.i18n.NativeLocaleDigits');
 
 /**
- * Datetime formatting functions following the pattern specification as defined
+ * IMPORTANT: Datetime formatting results different between JavaScript and
+ * native ECMAScript implementations.
+ *
+ * Native mode accepts a set of options for styles and also for specifying
+ * a small set of choices for each individual field of a formatted output. These
+ * effectively specify skeletons which direct the formatting according to
+ * formats built into the ECMAScript DateTime implementation of
+ * Intl.DateTimeFormat.
+ *
+ * The ECMAScript DateTimeFormat constructor and options are defined here:
+ * {@link
+ * https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DateTimeFormat}
+ *
+ * Datetime formatting functions in JavaScript mode are provided with
+ * options to use standard styles, predefined patterns such as YEAR_FULL,
+ * and other values in goog.i18n.DateTimeFormat.Format.
+ *
+ * Native mode date/time formatting is supported only for these standard
+ * patterns because they can be directly mapped to native mode options.
+ *
+ * Native mode does not support custom patterns, which are discouraged.
+ * Using such custom pattern strings will call the JavaScript (polyfill)
+ * version of DateTimeFormat rather than native ECMAScript.
+ *
+ * Custom patterns can be used using the symbols below for date/time.
+ * Other text can be included. However, standard patterns are preferred
+ * because native EMCAScript code is more efficient in download size and time.
+ *
+ * The following symbols may be used in pattern specification, as defined
  * in JDK, ICU and CLDR, with minor modification for typical usage in JS.
+ *
  * Pattern specification:
  * {@link http://userguide.icu-project.org/formatparse/datetime}
  * <pre>
@@ -97,9 +134,9 @@ goog.requireType('goog.i18n.DateTimeSymbolsType');
  *     or the common patterns defined in goog.i18n.DateTimePatterns.
  *     Examples:
  *     <code><pre>
- *       var fmt = new goog.i18n.DateTimeFormat(
+ *       let fmt = new goog.i18n.DateTimeFormat(
  *           goog.i18n.DateTimeFormat.Format.FULL_DATE);
- *       var fmt = new goog.i18n.DateTimeFormat(
+ *       let fmt = new goog.i18n.DateTimeFormat(
  *           goog.i18n.DateTimePatterns.MONTH_DAY_YEAR_MEDIUM);
  *     </pre></code>
  *
@@ -115,19 +152,46 @@ goog.i18n.DateTimeFormat = function(pattern, opt_dateTimeSymbols) {
           goog.i18n.DateTimeSymbols !== undefined,
       'goog.i18n.DateTimeSymbols or explicit symbols must be defined');
 
-  this.patternParts_ = [];
+  /**
+   * Remember if the implementation is ECMAScript
+   * @type {?goog.global.Intl.DateTimeFormat}
+   * @private
+   */
+  this.intlFormatter_ = null;
 
   /**
-   * Data structure that with all the locale info needed for date formatting.
-   * (day/month names, most common patterns, rules for week-end, etc.)
-   * @private {!goog.i18n.DateTimeSymbolsType}
+   * Remember the pattern applied for resetting Intl formatter.
+   * @type {number|string}
+   * @private @constant
    */
-  this.dateTimeSymbols_ = /** @type {!goog.i18n.DateTimeSymbolsType} */ (
-      opt_dateTimeSymbols || goog.i18n.DateTimeSymbols);
-  if (typeof pattern == 'number') {
-    this.applyStandardPattern_(pattern);
+  this.originalPattern_ = pattern;
+
+  this.patternParts_ = [];
+
+  // Try to look up pattern in the DateTimePattern data.
+  // If it is a standard value for the locale, then use the options
+  // with native formatter if possible
+
+  if (LocaleFeature.USE_ECMASCRIPT_I18N_DATETIMEF &&
+      ((typeof pattern == 'number'))) {
+    // Use Intl DateTimeFormat class with standard predefined- patterns
+    // Assumes no time zone settings
+    this.applyStandardEnumNative_(pattern, false, null);
   } else {
-    this.applyPattern_(pattern);
+    /**
+     * Use polyfill implementation with data defining locale-specific data such
+     * as (day/month names, most common patterns, rules for week-end, etc.)
+     * @private {!goog.i18n.DateTimeSymbolsType}
+     * @const
+     */
+    this.dateTimeSymbols_ = /** @type {!goog.i18n.DateTimeSymbolsType} */ (
+        opt_dateTimeSymbols || goog.i18n.DateTimeSymbols);
+    if (typeof pattern == 'number') {
+      this.applyStandardPattern_(pattern);
+    } else {
+      // Pattern is a string. This requires the polyfill implementation.
+      this.applyPattern_(pattern);
+    }
   }
 };
 
@@ -152,11 +216,10 @@ goog.i18n.DateTimeFormat.Format = {
   SHORT_DATETIME: 11
 };
 
-
 /**
  * regular expression pattern for parsing pattern string
- * @type {Array<RegExp>}
- * @private
+ * @type {!Array<!RegExp>}
+ * @private @const
  */
 goog.i18n.DateTimeFormat.TOKENS_ = [
   // quote string
@@ -204,11 +267,11 @@ goog.i18n.DateTimeFormat.prototype.applyPattern_ = function(pattern) {
   }
   // lex the pattern, once for all uses
   while (pattern) {
-    var previousPattern = pattern;
-    for (var i = 0; i < goog.i18n.DateTimeFormat.TOKENS_.length; ++i) {
-      var m = pattern.match(goog.i18n.DateTimeFormat.TOKENS_[i]);
+    const previousPattern = pattern;
+    for (let i = 0; i < goog.i18n.DateTimeFormat.TOKENS_.length; ++i) {
+      const m = pattern.match(goog.i18n.DateTimeFormat.TOKENS_[i]);
       if (m) {
-        var part = m[0];
+        let part = m[0];
         pattern = pattern.substring(part.length);
         if (i == goog.i18n.DateTimeFormat.PartTypes_.QUOTED_STRING) {
           if (part == '\'\'') {
@@ -234,8 +297,9 @@ goog.i18n.DateTimeFormat.prototype.applyPattern_ = function(pattern) {
 
 /**
  * Format the given date object according to preset pattern and current locale.
- * @param {goog.date.DateLike} date The Date object that is being formatted.
- * @param {goog.i18n.TimeZone=} opt_timeZone optional, if specified, time
+ * @param {?goog.date.DateLike|undefined} date The Date object that is being
+ *     formatted.
+ * @param {?goog.i18n.TimeZone=} opt_timeZone optional, if specified, time
  *    related fields will be formatted based on its setting. When this field
  *    is not specified, "undefined" will be pass around and those function
  *    that really need time zone service will create a default one.
@@ -262,46 +326,205 @@ goog.i18n.DateTimeFormat.prototype.format = function(date, opt_timeZone) {
   // our own code, we uses 3 Date object instead, one for "Year, month, day",
   // one for time within that day, and one for timeZone object since it need
   // the real time to figure out actual time zone offset.
-  var diff = opt_timeZone ?
-      (date.getTimezoneOffset() - opt_timeZone.getOffset(date)) * 60000 :
-      0;
-  var dateForDate = diff ? new Date(date.getTime() + diff) : date;
-  var dateForTime = dateForDate;
-  // When the time manipulation applied above spans the DST on/off hour, this
-  // could alter the time incorrectly by adding or subtracting an additional
-  // hour.
-  // We can mitigate this by:
-  // - Adding the difference in timezone offset to the date. This ensures that
-  //   the dateForDate is still within the right day if the extra DST hour
-  //   affected the date.
-  // - Move the time one day forward if we applied a timezone offset backwards,
-  //   or vice versa. This trick ensures that the time is in the same offset
-  //   as the original date, so we remove the additional hour added or
-  //   subtracted by the DST switch.
-  if (opt_timeZone &&
-      dateForDate.getTimezoneOffset() != date.getTimezoneOffset()) {
-    var dstDiff =
-        (dateForDate.getTimezoneOffset() - date.getTimezoneOffset()) * 60000;
-    dateForDate = new Date(dateForDate.getTime() + dstDiff);
-
-    diff += diff > 0 ? -goog.date.MS_PER_DAY : goog.date.MS_PER_DAY;
-    dateForTime = new Date(date.getTime() + diff);
-  }
 
-  var out = [];
-  for (var i = 0; i < this.patternParts_.length; ++i) {
-    var text = this.patternParts_[i].text;
-    if (goog.i18n.DateTimeFormat.PartTypes_.FIELD ==
-        this.patternParts_[i].type) {
-      out.push(this.formatField_(
-          text, date, dateForDate, dateForTime, opt_timeZone));
+  if (this.intlFormatter_ && LocaleFeature.USE_ECMASCRIPT_I18N_DATETIMEF) {
+    // Use Native ECMASCript formatting
+
+    // Compare the date for type UTC and formatter's timeZone setting.
+    let changedUtcSettings = false;
+    // Is the new date/time based on UTC or local time?
+    const isDateUtc = (date instanceof goog.date.UtcDateTime);
+    const options = this.intlFormatter_.resolvedOptions();
+    if (isDateUtc) {
+      changedUtcSettings = (options.timeZone !== 'UTC');
     } else {
-      out.push(text);
+      changedUtcSettings = (options.timeZone === 'UTC');
     }
+
+    if (goog.i18n.DateTimeFormat.resetEnforceAsciiDigits_ ||
+        changedUtcSettings || opt_timeZone) {
+      // Create new Intl DateTimeFormat object with reset values.
+      this.applyStandardEnumNative_(
+          this.originalPattern_, isDateUtc, opt_timeZone);
+      goog.i18n.DateTimeFormat.resetEnforceAsciiDigits_ = false;
+    }
+
+    /**
+     * @type {!Date|number|undefined} realdate type match for Closure
+     */
+    const realdate = date ? new Date(date.valueOf()) : undefined;
+
+    // To be consistent with polyfill results, use "UTC" instead of "GMT".
+    // return this.intlFormatter_.format(realdate).replace(/GMT-/, 'UTC-');
+    let result = this.intlFormatter_.format(realdate).replace(/GMT-/, 'UTC-');
+    return result;
+  } else {
+    // Format using polyfill.
+    let diff = opt_timeZone ?
+        (date.getTimezoneOffset() - opt_timeZone.getOffset(date)) * 60000 :
+        0;
+    let dateForDate = diff ? new Date(date.getTime() + diff) : date;
+    let dateForTime = dateForDate;
+    // When the time manipulation applied above spans the DST on/off hour, this
+    // could alter the time incorrectly by adding or subtracting an additional
+    // hour.
+    // We can mitigate this by:
+    // - Adding the difference in timezone offset to the date. This ensures that
+    //   the dateForDate is still within the right day if the extra DST hour
+    //   affected the date.
+    // - Move the time one day forward if we applied a timezone offset
+    // backwards,
+    //   or vice versa. This trick ensures that the time is in the same offset
+    //   as the original date, so we remove the additional hour added or
+    //   subtracted by the DST switch.
+    if (opt_timeZone &&
+        dateForDate.getTimezoneOffset() != date.getTimezoneOffset()) {
+      const dstDiff =
+          (dateForDate.getTimezoneOffset() - date.getTimezoneOffset()) * 60000;
+      dateForDate = new Date(dateForDate.getTime() + dstDiff);
+
+      diff += diff > 0 ? -goog.date.MS_PER_DAY : goog.date.MS_PER_DAY;
+      dateForTime = new Date(date.getTime() + diff);
+    }
+
+    const out = [];
+    for (let i = 0; i < this.patternParts_.length; ++i) {
+      const text = this.patternParts_[i].text;
+      if (goog.i18n.DateTimeFormat.PartTypes_.FIELD ==
+          this.patternParts_[i].type) {
+        out.push(this.formatField_(
+            text, date, dateForDate, dateForTime, opt_timeZone));
+      } else {
+        out.push(text);
+      }
+    }
+    return out.join('');
   }
-  return out.join('');
 };
 
+/**
+ * Parameters to Intl.DateTimeFormat constructor
+ * @private @typedef {{
+ *    calendar: (string|undefined),
+ *    dateStyle: (string|undefined),
+ *    timeStyle: (string|undefined),
+ *    era: (string|undefined),
+ *    formatMatcher: (string|undefined),
+ *    localeMatcher: (string|undefined),
+ *    year: (string|undefined),
+ *    month: (string|undefined),
+ *    day: (string|undefined),
+ *    weekday: (string|undefined),
+ *    hour: (string|undefined),
+ *    hour12: (boolean|undefined),
+ *    minute: (string|undefined),
+ *    second: (string|undefined),
+ *    timeZone: (string|undefined),
+ *    numberingSystem: (string|undefined),
+ *    timeZoneName: (string|undefined),
+ * }}
+ */
+goog.i18n.DateTimeFormat.IntlOptions;
+
+/**
+ * Create an ECMAScript Intl.DateTimeFormat object based on
+ * a predefined skeleton of fields and settings.
+ * @param {number|string} formatType A number that identified the predefined
+ *     pattern.
+ * @param {boolean} isUtc Should values be fixed in UTC?
+ * @param {?goog.i18n.TimeZone=} opt_timeZone explicit set time zone
+ * @private
+ */
+goog.i18n.DateTimeFormat.prototype.applyStandardEnumNative_ = function(
+    formatType, isUtc, opt_timeZone) {
+  /** @type {!goog.i18n.DateTimeFormat.IntlOptions} */
+  const options = {calendar: 'gregory'};  // Only Gregorian calendar
+
+  // When time zone is explicitly given
+  if (isUtc) {
+    options.timeZone = 'UTC';
+  } else if (opt_timeZone) {
+    options.timeZone = opt_timeZone.getTimeZoneId();
+  }
+
+  switch (formatType) {
+      // DATEFORMATS
+    case goog.i18n.DateTimeFormat.Format.FULL_DATE:
+      options.dateStyle = 'full';
+      break;
+    case goog.i18n.DateTimeFormat.Format.LONG_DATE:
+      options.dateStyle = 'long';
+      break;
+    case goog.i18n.DateTimeFormat.Format.MEDIUM_DATE:
+      options.dateStyle = 'medium';
+      break;
+    case goog.i18n.DateTimeFormat.Format.SHORT_DATE:
+    default:
+      options.dateStyle = 'short';
+      break;
+
+      // TIMEFORMATS
+    case goog.i18n.DateTimeFormat.Format.FULL_TIME:
+      options.timeStyle = 'full';
+      break;
+    case goog.i18n.DateTimeFormat.Format.LONG_TIME:
+      options.timeStyle = 'long';
+      break;
+    case goog.i18n.DateTimeFormat.Format.MEDIUM_TIME:
+      options.timeStyle = 'medium';
+      break;
+    case goog.i18n.DateTimeFormat.Format.SHORT_TIME:
+      options.timeStyle = 'short';
+      break;
+
+    // DATETIMEFORMATS
+    case goog.i18n.DateTimeFormat.Format.FULL_DATETIME:
+      options.dateStyle = 'full';
+      options.timeStyle = 'full';
+      // Can we modify how timezone is presented?
+      // if (opt_timeZone) {
+      //   options.timeZoneName = 'long';
+      // } else {
+      //   options.timeZoneName = 'short';
+      // }
+      break;
+    case goog.i18n.DateTimeFormat.Format.LONG_DATETIME:
+      options.dateStyle = 'long';
+      options.timeStyle = 'long';
+      break;
+    case goog.i18n.DateTimeFormat.Format.MEDIUM_DATETIME:
+      options.dateStyle = 'medium';
+      options.timeStyle = 'medium';
+      break;
+    case goog.i18n.DateTimeFormat.Format.SHORT_DATETIME:
+      options.dateStyle = 'short';
+      options.timeStyle = 'short';
+      break;
+  }
+
+
+  // Intl requires '-' instead of '_'.
+  let fixedLocale = goog.LOCALE.replace(/_/g, '-');
+  if (!goog.LOCALE) {
+    fixedLocale = 'en';  // The default
+  }
+
+  if (goog.i18n.DateTimeFormat.enforceAsciiDigits_) {
+    options.numberingSystem = 'latn';
+  } else {
+    if (fixedLocale in NativeLocaleDigits.FormatWithLocaleDigits) {
+      options.numberingSystem =
+          NativeLocaleDigits.FormatWithLocaleDigits[fixedLocale];
+    }
+  }
+
+  try {
+    this.intlFormatter_ =
+        new goog.global.Intl.DateTimeFormat(fixedLocale, options);
+  } catch (e) {
+    goog.asserts.assert(e != null);
+  }
+};
 
 /**
  * Apply a predefined pattern as identified by formatType, which is stored in
@@ -312,7 +535,7 @@ goog.i18n.DateTimeFormat.prototype.format = function(date, opt_timeZone) {
 goog.i18n.DateTimeFormat.prototype.applyStandardPattern_ = function(
     formatType) {
   'use strict';
-  var pattern;
+  let pattern;
   if (formatType < 4) {
     pattern = this.dateTimeSymbols_.DATEFORMATS[formatType];
   } else if (formatType < 8) {
@@ -330,7 +553,6 @@ goog.i18n.DateTimeFormat.prototype.applyStandardPattern_ = function(
   this.applyPattern_(pattern);
 };
 
-
 /**
  * Localizes a string potentially containing numbers, replacing ASCII digits
  * with native digits if specified so by the locale. Leaves other characters.
@@ -352,6 +574,13 @@ goog.i18n.DateTimeFormat.prototype.localizeNumbers_ = function(input) {
 goog.i18n.DateTimeFormat.enforceAsciiDigits_ = false;
 
 
+/**
+ * Records if ASCII digits was set after formatter construction.
+ * @type {boolean}
+ * @private
+ */
+goog.i18n.DateTimeFormat.resetEnforceAsciiDigits_ = false;
+
 /**
  * If RLM unicode characters should be removed from date/time patterns (useful
  * when enforcing ASCII digits for Arabic). See `#setEnforceAsciiDigits`.
@@ -377,7 +606,11 @@ goog.i18n.DateTimeFormat.removeRlmInPatterns_ = false;
  */
 goog.i18n.DateTimeFormat.setEnforceAsciiDigits = function(enforceAsciiDigits) {
   'use strict';
-  goog.i18n.DateTimeFormat.enforceAsciiDigits_ = enforceAsciiDigits;
+  if (goog.i18n.DateTimeFormat.enforceAsciiDigits_ !== enforceAsciiDigits) {
+    goog.i18n.DateTimeFormat.enforceAsciiDigits_ = enforceAsciiDigits;
+    // And remember for resetting native formatter.
+    goog.i18n.DateTimeFormat.resetEnforceAsciiDigits_ = true;
+  }
 
   // Also setting removal of RLM chracters when forcing ASCII digits since it's
   // the right thing to do for Arabic standard patterns. One could add an
@@ -410,15 +643,15 @@ goog.i18n.DateTimeFormat.localizeNumbers = function(
     input, opt_dateTimeSymbols) {
   'use strict';
   input = String(input);
-  var dateTimeSymbols = opt_dateTimeSymbols || goog.i18n.DateTimeSymbols;
+  const dateTimeSymbols = opt_dateTimeSymbols || goog.i18n.DateTimeSymbols;
   if (dateTimeSymbols.ZERODIGIT === undefined ||
       goog.i18n.DateTimeFormat.enforceAsciiDigits_) {
     return input;
   }
 
-  var parts = [];
-  for (var i = 0; i < input.length; i++) {
-    var c = input.charCodeAt(i);
+  const parts = [];
+  for (let i = 0; i < input.length; i++) {
+    const c = input.charCodeAt(i);
     parts.push(
         (0x30 <= c && c <= 0x39) ?  // '0' <= c <= '9'
             String.fromCharCode(dateTimeSymbols.ZERODIGIT + c - 0x30) :
@@ -439,7 +672,7 @@ goog.i18n.DateTimeFormat.localizeNumbers = function(
  */
 goog.i18n.DateTimeFormat.prototype.formatEra_ = function(count, date) {
   'use strict';
-  var value = date.getFullYear() > 0 ? 1 : 0;
+  const value = date.getFullYear() > 0 ? 1 : 0;
   return count >= 4 ? this.dateTimeSymbols_.ERANAMES[value] :
                       this.dateTimeSymbols_.ERAS[value];
 };
@@ -460,7 +693,7 @@ goog.i18n.DateTimeFormat.prototype.formatEra_ = function(count, date) {
  */
 goog.i18n.DateTimeFormat.prototype.formatYear_ = function(count, date) {
   'use strict';
-  var value = date.getFullYear();
+  let value = date.getFullYear();
   if (value < 0) {
     value = -value;
   }
@@ -490,7 +723,7 @@ goog.i18n.DateTimeFormat.prototype.formatYear_ = function(count, date) {
  */
 goog.i18n.DateTimeFormat.prototype.formatYearOfWeek_ = function(count, date) {
   'use strict';
-  var value = goog.date.getYearOfWeek(
+  let value = goog.date.getYearOfWeek(
       date.getFullYear(), date.getMonth(), date.getDate(),
       this.dateTimeSymbols_.FIRSTWEEKCUTOFFDAY,
       this.dateTimeSymbols_.FIRSTDAYOFWEEK);
@@ -520,7 +753,7 @@ goog.i18n.DateTimeFormat.prototype.formatYearOfWeek_ = function(count, date) {
  */
 goog.i18n.DateTimeFormat.prototype.formatMonth_ = function(count, date) {
   'use strict';
-  var value = date.getMonth();
+  const value = date.getMonth();
   switch (count) {
     case 5:
       return this.dateTimeSymbols_.NARROWMONTHS[value];
@@ -566,7 +799,7 @@ goog.i18n.DateTimeFormat.validateDateHasTime_ = function(date) {
 goog.i18n.DateTimeFormat.prototype.format24Hours_ = function(count, date) {
   'use strict';
   goog.i18n.DateTimeFormat.validateDateHasTime_(date);
-  var hours = goog.i18n.DateTimeFormat.getHours_(date) || 24;
+  const hours = goog.i18n.DateTimeFormat.getHours_(date) || 24;
   return this.localizeNumbers_(goog.string.padNumber(hours, count));
 };
 
@@ -586,7 +819,7 @@ goog.i18n.DateTimeFormat.prototype.formatFractionalSeconds_ = function(
     count, date) {
   'use strict';
   // Fractional seconds left-justify, append 0 for precision beyond 3
-  var value = date.getMilliseconds() / 1000;
+  const value = date.getMilliseconds() / 1000;
   return this.localizeNumbers_(
       value.toFixed(Math.min(3, count)).substr(2) +
       (count > 3 ? goog.string.padNumber(0, count - 3) : ''));
@@ -604,7 +837,7 @@ goog.i18n.DateTimeFormat.prototype.formatFractionalSeconds_ = function(
  */
 goog.i18n.DateTimeFormat.prototype.formatDayOfWeek_ = function(count, date) {
   'use strict';
-  var value = date.getDay();
+  const value = date.getDay();
   return count >= 4 ? this.dateTimeSymbols_.WEEKDAYS[value] :
                       this.dateTimeSymbols_.SHORTWEEKDAYS[value];
 };
@@ -622,7 +855,7 @@ goog.i18n.DateTimeFormat.prototype.formatDayOfWeek_ = function(count, date) {
 goog.i18n.DateTimeFormat.prototype.formatAmPm_ = function(count, date) {
   'use strict';
   goog.i18n.DateTimeFormat.validateDateHasTime_(date);
-  var hours = goog.i18n.DateTimeFormat.getHours_(date);
+  const hours = goog.i18n.DateTimeFormat.getHours_(date);
   return this.dateTimeSymbols_.AMPMS[hours >= 12 && hours < 24 ? 1 : 0];
 };
 
@@ -639,7 +872,7 @@ goog.i18n.DateTimeFormat.prototype.formatAmPm_ = function(count, date) {
 goog.i18n.DateTimeFormat.prototype.format1To12Hours_ = function(count, date) {
   'use strict';
   goog.i18n.DateTimeFormat.validateDateHasTime_(date);
-  var hours = goog.i18n.DateTimeFormat.getHours_(date) % 12 || 12;
+  const hours = goog.i18n.DateTimeFormat.getHours_(date) % 12 || 12;
   return this.localizeNumbers_(goog.string.padNumber(hours, count));
 };
 
@@ -656,7 +889,7 @@ goog.i18n.DateTimeFormat.prototype.format1To12Hours_ = function(count, date) {
 goog.i18n.DateTimeFormat.prototype.format0To11Hours_ = function(count, date) {
   'use strict';
   goog.i18n.DateTimeFormat.validateDateHasTime_(date);
-  var hours = goog.i18n.DateTimeFormat.getHours_(date) % 12;
+  const hours = goog.i18n.DateTimeFormat.getHours_(date) % 12;
   return this.localizeNumbers_(goog.string.padNumber(hours, count));
 };
 
@@ -673,7 +906,7 @@ goog.i18n.DateTimeFormat.prototype.format0To11Hours_ = function(count, date) {
 goog.i18n.DateTimeFormat.prototype.format0To23Hours_ = function(count, date) {
   'use strict';
   goog.i18n.DateTimeFormat.validateDateHasTime_(date);
-  var hours = goog.i18n.DateTimeFormat.getHours_(date);
+  const hours = goog.i18n.DateTimeFormat.getHours_(date);
   return this.localizeNumbers_(goog.string.padNumber(hours, count));
 };
 
@@ -690,7 +923,7 @@ goog.i18n.DateTimeFormat.prototype.format0To23Hours_ = function(count, date) {
 goog.i18n.DateTimeFormat.prototype.formatStandaloneDay_ = function(
     count, date) {
   'use strict';
-  var value = date.getDay();
+  const value = date.getDay();
   switch (count) {
     case 5:
       return this.dateTimeSymbols_.STANDALONENARROWWEEKDAYS[value];
@@ -716,7 +949,7 @@ goog.i18n.DateTimeFormat.prototype.formatStandaloneDay_ = function(
 goog.i18n.DateTimeFormat.prototype.formatStandaloneMonth_ = function(
     count, date) {
   'use strict';
-  var value = date.getMonth();
+  const value = date.getMonth();
   switch (count) {
     case 5:
       return this.dateTimeSymbols_.STANDALONENARROWMONTHS[value];
@@ -741,7 +974,7 @@ goog.i18n.DateTimeFormat.prototype.formatStandaloneMonth_ = function(
  */
 goog.i18n.DateTimeFormat.prototype.formatQuarter_ = function(count, date) {
   'use strict';
-  var value = Math.floor(date.getMonth() / 3);
+  const value = Math.floor(date.getMonth() / 3);
   return count < 4 ? this.dateTimeSymbols_.SHORTQUARTERS[value] :
                      this.dateTimeSymbols_.QUARTERS[value];
 };
@@ -807,7 +1040,7 @@ goog.i18n.DateTimeFormat.prototype.formatSeconds_ = function(count, date) {
  */
 goog.i18n.DateTimeFormat.prototype.formatWeekOfYear_ = function(count, date) {
   'use strict';
-  var weekNum = goog.date.getWeekNumber(
+  const weekNum = goog.date.getWeekNumber(
       date.getFullYear(), date.getMonth(), date.getDate(),
       this.dateTimeSymbols_.FIRSTWEEKCUTOFFDAY,
       this.dateTimeSymbols_.FIRSTDAYOFWEEK);
@@ -822,7 +1055,7 @@ goog.i18n.DateTimeFormat.prototype.formatWeekOfYear_ = function(count, date) {
  * @param {number} count Number of time pattern char repeats, it controls
  *     how a field should be formatted.
  * @param {!goog.date.DateLike} date It holds the date object to be formatted.
- * @param {goog.i18n.TimeZone=} opt_timeZone This holds current time zone info.
+ * @param {?goog.i18n.TimeZone=} opt_timeZone This holds current time zone info.
  * @return {string} Formatted string that represent this field.
  * @private
  */
@@ -844,7 +1077,7 @@ goog.i18n.DateTimeFormat.prototype.formatTimeZoneRFC_ = function(
  * @param {number} count Number of time pattern char repeats, it controls
  *     how a field should be formatted.
  * @param {!goog.date.DateLike} date Whose value being evaluated.
- * @param {goog.i18n.TimeZone=} opt_timeZone This holds current time zone info.
+ * @param {?goog.i18n.TimeZone=} opt_timeZone This holds current time zone info.
  * @return {string} GMT timeZone string.
  * @private
  */
@@ -861,7 +1094,7 @@ goog.i18n.DateTimeFormat.prototype.formatTimeZone_ = function(
 /**
  * Generate GMT timeZone string for given date
  * @param {!goog.date.DateLike} date Whose value being evaluated.
- * @param {goog.i18n.TimeZone=} opt_timeZone This holds current time zone info.
+ * @param {?goog.i18n.TimeZone=} opt_timeZone This holds current time zone info.
  * @return {string} GMT timeZone string.
  * @private
  */
@@ -879,7 +1112,7 @@ goog.i18n.DateTimeFormat.prototype.formatTimeZoneId_ = function(
  * @param {number} count Number of time pattern char repeats, it controls
  *     how a field should be formatted.
  * @param {!goog.date.DateLike} date Whose value being evaluated.
- * @param {goog.i18n.TimeZone=} opt_timeZone This holds current time zone info.
+ * @param {?goog.i18n.TimeZone=} opt_timeZone This holds current time zone info.
  * @return {string} GMT timeZone string.
  * @private
  */
@@ -901,14 +1134,14 @@ goog.i18n.DateTimeFormat.prototype.formatTimeZoneLocationId_ = function(
  *     for formatting.
  * @param {!goog.date.DateLike} dateForTime used to resolve time fields
  *     for formatting.
- * @param {goog.i18n.TimeZone=} opt_timeZone This holds current time zone info.
+ * @param {?goog.i18n.TimeZone=} opt_timeZone This holds current time zone info.
  * @return {string} string representation for the given field.
  * @private
  */
 goog.i18n.DateTimeFormat.prototype.formatField_ = function(
     patternStr, date, dateForDate, dateForTime, opt_timeZone) {
   'use strict';
-  var count = patternStr.length;
+  const count = patternStr.length;
   switch (patternStr.charAt(0)) {
     case 'G':
       return this.formatEra_(count, dateForDate);
@@ -957,4 +1190,6 @@ goog.i18n.DateTimeFormat.prototype.formatField_ = function(
     default:
       return '';
   }
+
 };
+});  // End of scope for module data
diff --git a/closure/goog/i18n/datetimeformat_test.js b/closure/goog/i18n/datetimeformat_test.js
index 86e1b205c2..861134f62f 100644
--- a/closure/goog/i18n/datetimeformat_test.js
+++ b/closure/goog/i18n/datetimeformat_test.js
@@ -11,6 +11,14 @@
 goog.module('goog.i18n.DateTimeFormatTest');
 goog.setTestOnly();
 
+
+const LocaleFeature = goog.require('goog.i18n.LocaleFeature');
+const PropertyReplacer = goog.require('goog.testing.PropertyReplacer');
+
+// Note that exact formatted output equivalence between Closure and
+// ECMAScript implementations is not required in all cases.
+const replacer = new PropertyReplacer();
+
 const DateDate = goog.require('goog.date.Date');
 const DateTime = goog.require('goog.date.DateTime');
 const DateTimeFormat = goog.require('goog.i18n.DateTimeFormat');
@@ -29,9 +37,12 @@ const DateTimePatterns_zh_HK = goog.require('goog.i18n.DateTimePatterns_zh_HK');
 const DateTimePatterns_zh_Hant_TW = goog.require('goog.i18n.DateTimePatterns_zh_Hant_TW');
 /** @suppress {extraRequire} */
 const DateTimeSymbols = goog.require('goog.i18n.DateTimeSymbols');
+const DateTimeSymbols_ar = goog.require('goog.i18n.DateTimeSymbols_ar');
 const DateTimeSymbols_ar_AE = goog.require('goog.i18n.DateTimeSymbols_ar_AE');
 const DateTimeSymbols_ar_EG = goog.require('goog.i18n.DateTimeSymbols_ar_EG');
 const DateTimeSymbols_ar_SA = goog.require('goog.i18n.DateTimeSymbols_ar_SA');
+const DateTimeSymbols_bg = goog.require('goog.i18n.DateTimeSymbols_bg');
+const DateTimeSymbols_bn = goog.require('goog.i18n.DateTimeSymbols_bn');
 const DateTimeSymbols_bn_BD = goog.require('goog.i18n.DateTimeSymbols_bn_BD');
 const DateTimeSymbols_de = goog.require('goog.i18n.DateTimeSymbols_de');
 const DateTimeSymbols_en = goog.require('goog.i18n.DateTimeSymbols_en');
@@ -39,19 +50,74 @@ const DateTimeSymbols_en_GB = goog.require('goog.i18n.DateTimeSymbols_en_GB');
 const DateTimeSymbols_en_IE = goog.require('goog.i18n.DateTimeSymbols_en_IE');
 const DateTimeSymbols_en_IN = goog.require('goog.i18n.DateTimeSymbols_en_IN');
 const DateTimeSymbols_en_US = goog.require('goog.i18n.DateTimeSymbols_en_US');
+const DateTimeSymbols_en_XA = goog.require('goog.i18n.DateTimeSymbols_en_XA');
 const DateTimeSymbols_fa = goog.require('goog.i18n.DateTimeSymbols_fa');
 const DateTimeSymbols_fr = goog.require('goog.i18n.DateTimeSymbols_fr');
 const DateTimeSymbols_fr_DJ = goog.require('goog.i18n.DateTimeSymbols_fr_DJ');
 const DateTimeSymbols_he_IL = goog.require('goog.i18n.DateTimeSymbols_he_IL');
 const DateTimeSymbols_ja = goog.require('goog.i18n.DateTimeSymbols_ja');
+const DateTimeSymbols_ml = goog.require('goog.i18n.DateTimeSymbols_ml');
+const DateTimeSymbols_mr = goog.require('goog.i18n.DateTimeSymbols_mr');
+const DateTimeSymbols_my = goog.require('goog.i18n.DateTimeSymbols_my');
+const DateTimeSymbols_ne = goog.require('goog.i18n.DateTimeSymbols_ne');
 const DateTimeSymbols_ro_RO = goog.require('goog.i18n.DateTimeSymbols_ro_RO');
 const DateTimeSymbols_sv = goog.require('goog.i18n.DateTimeSymbols_sv');
+const DateTimeSymbols_zh_HK = goog.require('goog.i18n.DateTimeSymbols_zh_HK');
+const DateTimeSymbols_zh_Hant_TW = goog.require('goog.i18n.DateTimeSymbols_zh_Hant_TW');
 const TimeZone = goog.require('goog.i18n.TimeZone');
+
+const UtcDateTime = goog.require('goog.date.UtcDateTime');
+
 const testSuite = goog.require('goog.testing.testSuite');
 
 // Initial values
-goog.i18n.DateTimePatterns = DateTimePatterns_en;
-goog.i18n.DateTimeSymbols = DateTimeSymbols_en;
+replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_en);
+replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_en);
+
+// Helpers for native mode
+/**
+ * Changes status of ECMASCRIPT mode
+ * @param {boolean} new_setting
+ */
+function setNativeMode(new_setting) {
+  replacer.set(LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', new_setting);
+}
+
+// Sets up goog.USE_ECMASCRIPT_I18N_DATETIMEF flag in each function.
+let testECMAScriptOptions = [false];
+// Don't test native ECMASCript on IE11.
+if (Intl.DateTimeFormat) {
+  // Add test if the browser environment supports ECMAScript implementation.
+  if (!goog.labs.userAgent.browser.isIE()) {
+    testECMAScriptOptions.push(true);
+  }
+}
+
+/**
+ * Gets current setting for native ECMAScript mode
+ * @return {boolean}
+ */
+function getNativeMode() {
+  return LocaleFeature.USE_ECMASCRIPT_I18N_DATETIMEF;
+}
+
+/**
+ * Returns string without RTL or LTR markers.
+ * @param {string} input
+ * @return {string}
+ */
+function removeDirectionMarkers(input) {
+  return input.replace(/[\u200e\u200f]/g, '');
+}
+
+/**
+ * Returns string without LTR markers.
+ * @param {string} input
+ * @return {string}
+ */
+function removeLtrMarkers(input) {
+  return input.replace(/[\u200e]/g, '');
+}
 
 /**
  * Helpers to make tests work regardless of the timeZone we're in.
@@ -168,8 +234,6 @@ const europeBerlinData = {
   'std_offset': 60,
 };
 
-let date;
-
 /**
  * Creates a string by concatenating the week number for 7 successive days
  * @return {string}
@@ -186,488 +250,719 @@ function weekInYearFor7Days() {
 }
 
 testSuite({
+  getTestName: function() {
+    return 'DateTimeFormat Tests';
+  },
+
+  setUpPage() {},
+
+  setUp() {
+    replacer.set(LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', false);
+    setNativeMode(false);
+    replacer.replace(goog, 'LOCALE', 'en');
+    replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_en);
+    replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_en);
+  },
+
   tearDown() {
     // We always revert to a known state
-    goog.i18n.DateTimePatterns = DateTimePatterns_en;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_en;
+    replacer.replace(goog, 'LOCALE', 'en');
     DateTimeFormat.setEnforceAsciiDigits(false);
+
+    replacer.reset();
+
+    // Reset to non-native
+    setNativeMode(false);
   },
 
   testHHmmss() {
-    goog.i18n.DateTimePatterns = DateTimePatterns_de;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_de;
-    date = new Date(2006, 6, 27, 13, 10, 10, 250);
-    const fmt = new DateTimeFormat('HH:mm:ss');
-    assertEquals('13:10:10', fmt.format(date));
+    replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_de);
+    replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_de);
+    const date = new Date(2006, 6, 27, 13, 10, 10, 250);
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+
+      const fmt = new DateTimeFormat('HH:mm:ss');
+      assertEquals('13:10:10', fmt.format(date));
+    }
   },
 
   testhhmmssa() {
-    goog.i18n.DateTimePatterns = DateTimePatterns_de;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_de;
-    date = new Date(2006, 6, 27, 13, 10, 10, 250);
-    const fmt = new DateTimeFormat('h:mm:ss a');
-    assertEquals('1:10:10 PM', fmt.format(date));
+    replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_de);
+    replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_de);
+    const date = new Date(2006, 6, 27, 13, 10, 10, 250);
+    for (let nativeMode of testECMAScriptOptions) {
+      setNativeMode(nativeMode);
+      const fmt = new DateTimeFormat('h:mm:ss a');
+      assertEquals('1:10:10 PM', fmt.format(date));
+    }
   },
 
   testEEEMMMddyy() {
-    goog.i18n.DateTimePatterns = DateTimePatterns_de;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_de;
-    date = new Date(2006, 6, 27, 13, 10, 10, 250);
-    const fmt = new DateTimeFormat('EEE, MMM d, yy');
-    assertEquals('Do., Juli 27, 06', fmt.format(date));
+    const date = new Date(2006, 6, 27, 13, 10, 10, 250);
+    replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_de);
+    replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_de);
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+      const fmt = new DateTimeFormat('EEE, MMM d, yy');
+      assertEquals('Do., Juli 27, 06', fmt.format(date));
+    }
   },
 
   testEEEEMMMddyy() {
-    goog.i18n.DateTimePatterns = DateTimePatterns_de;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_de;
-    date = new Date(2006, 6, 27, 13, 10, 10, 250);
-    const fmt = new DateTimeFormat('EEEE,MMMM dd, yyyy');
-    assertEquals('Donnerstag,Juli 27, 2006', fmt.format(date));
+    const date = new Date(2006, 6, 27, 13, 10, 10, 250);
+    replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_de);
+    replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_de);
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+      const fmt = new DateTimeFormat('EEEE,MMMM dd, yyyy');
+      assertEquals('Donnerstag,Juli 27, 2006', fmt.format(date));
+    }
   },
 
   testyyyyMMddG() {
-    goog.i18n.DateTimePatterns = DateTimePatterns_de;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_de;
-    date = new Date(Date.UTC(2006, 6, 27, 13, 10, 10, 250));
-    /** @suppress {checkTypes} suppression added to enable type checking */
-    const timeZone = TimeZone.createTimeZone(420, DateTimeSymbols_de);
-    const fmt = new DateTimeFormat('yyyy.MM.dd G \'at\' HH:mm:ss vvvv');
-    assertEquals(
-        '2006.07.27 n. Chr. at 06:10:10 Etc/GMT+7', fmt.format(date, timeZone));
+    const date = new Date(Date.UTC(2006, 6, 27, 13, 10, 10, 250));
+    replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_de);
+    replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_de);
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+      /** @suppress {checkTypes} suppression added to enable type checking */
+      const timeZone = TimeZone.createTimeZone(420, DateTimeSymbols_de);
+      const fmt = new DateTimeFormat('yyyy.MM.dd G \'at\' HH:mm:ss vvvv');
+      assertEquals(
+          '2006.07.27 n. Chr. at 06:10:10 Etc/GMT+7',
+          fmt.format(date, timeZone));
+    }
   },
 
   testyyyyyMMMMM() {
-    goog.i18n.DateTimePatterns = DateTimePatterns_de;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_de;
-    date = new Date(2006, 6, 27, 13, 10, 10, 250);
-    let fmt = new DateTimeFormat('yyyyy.MMMMM.dd GGG hh:mm aaa');
-    assertEquals('02006.J.27 n. Chr. 01:10 PM', fmt.format(date));
-
-    date = new Date(972, 11, 25, 13, 10, 10, 250);
-    fmt = new DateTimeFormat('yyyyy.MMMMM.dd');
-    assertEquals('00972.D.25', fmt.format(date));
+    replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_de);
+    replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_de);
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+      let date = new Date(2006, 6, 27, 13, 10, 10, 250);
+      let fmt = new DateTimeFormat('yyyyy.MMMMM.dd GGG hh:mm aaa');
+      assertEquals('02006.J.27 n. Chr. 01:10 PM', fmt.format(date));
+
+      date = new Date(972, 11, 25, 13, 10, 10, 250);
+      fmt = new DateTimeFormat('yyyyy.MMMMM.dd');
+      assertEquals('00972.D.25', fmt.format(date));
+    }
   },
 
   testQQQQyy() {
-    goog.i18n.DateTimePatterns = DateTimePatterns_de;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_de;
-    date = new Date(2006, 0, 27, 13, 10, 10, 250);
-    const fmt = new DateTimeFormat('QQQQ yy');
-    assertEquals('1. Quartal 06', fmt.format(date));
-    date = new Date(2006, 1, 27, 13, 10, 10, 250);
-    assertEquals('1. Quartal 06', fmt.format(date));
-    date = new Date(2006, 2, 27, 13, 10, 10, 250);
-    assertEquals('1. Quartal 06', fmt.format(date));
-    date = new Date(2006, 3, 27, 13, 10, 10, 250);
-    assertEquals('2. Quartal 06', fmt.format(date));
-    date = new Date(2006, 4, 27, 13, 10, 10, 250);
-    assertEquals('2. Quartal 06', fmt.format(date));
-    date = new Date(2006, 5, 27, 13, 10, 10, 250);
-    assertEquals('2. Quartal 06', fmt.format(date));
-    date = new Date(2006, 6, 27, 13, 10, 10, 250);
-    assertEquals('3. Quartal 06', fmt.format(date));
-    date = new Date(2006, 7, 27, 13, 10, 10, 250);
-    assertEquals('3. Quartal 06', fmt.format(date));
-    date = new Date(2006, 8, 27, 13, 10, 10, 250);
-    assertEquals('3. Quartal 06', fmt.format(date));
-    date = new Date(2006, 9, 27, 13, 10, 10, 250);
-    assertEquals('4. Quartal 06', fmt.format(date));
-    date = new Date(2006, 10, 27, 13, 10, 10, 250);
-    assertEquals('4. Quartal 06', fmt.format(date));
-    date = new Date(2006, 11, 27, 13, 10, 10, 250);
-    assertEquals('4. Quartal 06', fmt.format(date));
+    replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_de);
+    replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_de);
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+
+      let date = new Date(2006, 0, 27, 13, 10, 10, 250);
+      const fmt = new DateTimeFormat('QQQQ yy');
+      assertEquals('1. Quartal 06', fmt.format(date));
+      date = new Date(2006, 1, 27, 13, 10, 10, 250);
+      assertEquals('1. Quartal 06', fmt.format(date));
+      date = new Date(2006, 2, 27, 13, 10, 10, 250);
+      assertEquals('1. Quartal 06', fmt.format(date));
+      date = new Date(2006, 3, 27, 13, 10, 10, 250);
+      assertEquals('2. Quartal 06', fmt.format(date));
+      date = new Date(2006, 4, 27, 13, 10, 10, 250);
+      assertEquals('2. Quartal 06', fmt.format(date));
+      date = new Date(2006, 5, 27, 13, 10, 10, 250);
+      assertEquals('2. Quartal 06', fmt.format(date));
+      date = new Date(2006, 6, 27, 13, 10, 10, 250);
+      assertEquals('3. Quartal 06', fmt.format(date));
+      date = new Date(2006, 7, 27, 13, 10, 10, 250);
+      assertEquals('3. Quartal 06', fmt.format(date));
+      date = new Date(2006, 8, 27, 13, 10, 10, 250);
+      assertEquals('3. Quartal 06', fmt.format(date));
+      date = new Date(2006, 9, 27, 13, 10, 10, 250);
+      assertEquals('4. Quartal 06', fmt.format(date));
+      date = new Date(2006, 10, 27, 13, 10, 10, 250);
+      assertEquals('4. Quartal 06', fmt.format(date));
+      date = new Date(2006, 11, 27, 13, 10, 10, 250);
+      assertEquals('4. Quartal 06', fmt.format(date));
+    }
   },
 
   testQQyyyy() {
-    goog.i18n.DateTimePatterns = DateTimePatterns_de;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_de;
-    date = new Date(2006, 0, 27, 13, 10, 10, 250);
-    const fmt = new DateTimeFormat('QQ yyyy');
-    assertEquals('Q1 2006', fmt.format(date));
-    date = new Date(2006, 1, 27, 13, 10, 10, 250);
-    assertEquals('Q1 2006', fmt.format(date));
-    date = new Date(2006, 2, 27, 13, 10, 10, 250);
-    assertEquals('Q1 2006', fmt.format(date));
-    date = new Date(2006, 3, 27, 13, 10, 10, 250);
-    assertEquals('Q2 2006', fmt.format(date));
-    date = new Date(2006, 4, 27, 13, 10, 10, 250);
-    assertEquals('Q2 2006', fmt.format(date));
-    date = new Date(2006, 5, 27, 13, 10, 10, 250);
-    assertEquals('Q2 2006', fmt.format(date));
-    date = new Date(2006, 6, 27, 13, 10, 10, 250);
-    assertEquals('Q3 2006', fmt.format(date));
-    date = new Date(2006, 7, 27, 13, 10, 10, 250);
-    assertEquals('Q3 2006', fmt.format(date));
-    date = new Date(2006, 8, 27, 13, 10, 10, 250);
-    assertEquals('Q3 2006', fmt.format(date));
-    date = new Date(2006, 9, 27, 13, 10, 10, 250);
-    assertEquals('Q4 2006', fmt.format(date));
-    date = new Date(2006, 10, 27, 13, 10, 10, 250);
-    assertEquals('Q4 2006', fmt.format(date));
-    date = new Date(2006, 11, 27, 13, 10, 10, 250);
-    assertEquals('Q4 2006', fmt.format(date));
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+      replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_de);
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_de);
+      let date = new Date(2006, 0, 27, 13, 10, 10, 250);
+      const fmt = new DateTimeFormat('QQ yyyy');
+      assertEquals('Q1 2006', fmt.format(date));
+      date = new Date(2006, 1, 27, 13, 10, 10, 250);
+      assertEquals('Q1 2006', fmt.format(date));
+      date = new Date(2006, 2, 27, 13, 10, 10, 250);
+      assertEquals('Q1 2006', fmt.format(date));
+      date = new Date(2006, 3, 27, 13, 10, 10, 250);
+      assertEquals('Q2 2006', fmt.format(date));
+      date = new Date(2006, 4, 27, 13, 10, 10, 250);
+      assertEquals('Q2 2006', fmt.format(date));
+      date = new Date(2006, 5, 27, 13, 10, 10, 250);
+      assertEquals('Q2 2006', fmt.format(date));
+      date = new Date(2006, 6, 27, 13, 10, 10, 250);
+      assertEquals('Q3 2006', fmt.format(date));
+      date = new Date(2006, 7, 27, 13, 10, 10, 250);
+      assertEquals('Q3 2006', fmt.format(date));
+      date = new Date(2006, 8, 27, 13, 10, 10, 250);
+      assertEquals('Q3 2006', fmt.format(date));
+      date = new Date(2006, 9, 27, 13, 10, 10, 250);
+      assertEquals('Q4 2006', fmt.format(date));
+      date = new Date(2006, 10, 27, 13, 10, 10, 250);
+      assertEquals('Q4 2006', fmt.format(date));
+      date = new Date(2006, 11, 27, 13, 10, 10, 250);
+      assertEquals('Q4 2006', fmt.format(date));
+    }
   },
 
   /** @suppress {checkTypes} suppression added to enable type checking */
   testMMddyyyyHHmmsszzz() {
-    goog.i18n.DateTimePatterns = DateTimePatterns_de;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_de;
-    date = new Date(2006, 6, 27, 13, 10, 10, 250);
-    const fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss zzz');
-    assertEquals(
-        '07/27/2006 13:10:10 ' + timezoneString(date), fmt.format(date));
+    const date = new Date(2006, 6, 27, 13, 10, 10, 250);
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+      replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_de);
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_de);
+      const fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss zzz');
+      assertEquals(
+          '07/27/2006 13:10:10 ' + timezoneString(date), fmt.format(date));
+    }
   },
 
   /** @suppress {checkTypes} suppression added to enable type checking */
   testMMddyyyyHHmmssZ() {
-    goog.i18n.DateTimePatterns = DateTimePatterns_de;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_de;
-    date = new Date(2006, 6, 27, 13, 10, 10, 250);
-    const fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss Z');
-    assertEquals(
-        '07/27/2006 13:10:10 ' + timezoneStringRFC(date), fmt.format(date));
+    const date = new Date(2006, 6, 27, 13, 10, 10, 250);
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+      replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_de);
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_de);
+      const fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss Z');
+
+      assertEquals(
+          '07/27/2006 13:10:10 ' + timezoneStringRFC(date), fmt.format(date));
+    }
   },
 
   testPatternMonthDayMedium() {
-    goog.i18n.DateTimePatterns = DateTimePatterns_de;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_de;
-    date = new Date(2006, 6, 27, 13, 10, 10, 250);
-    const fmt = new DateTimeFormat(goog.i18n.DateTimePatterns.MONTH_DAY_MEDIUM);
-    assertEquals('27. Juli', fmt.format(date));
+    const date = new Date(2006, 6, 27, 13, 10, 10, 250);
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+      replacer.replace(goog, 'LOCALE', 'de');
+      replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_de);
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_de);
+
+      const fmt = new DateTimeFormat(DateTimePatterns_de.MONTH_DAY_MEDIUM);
+      assertEquals('27. Juli', fmt.format(date));
+    }
   },
 
   testPatternYearMonthNarrow() {
-    goog.i18n.DateTimePatterns = DateTimePatterns_de;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_de;
-    date = new Date(2006, 6, 27, 13, 10, 10, 250);
-    const fmt = new DateTimeFormat(goog.i18n.DateTimePatterns.YEAR_MONTH_SHORT);
-    assertEquals('07.2006', fmt.format(date));
+    replacer.replace(goog, 'LOCALE', 'de');
+    replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_de);
+    replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_de);
+    const date = new Date(2006, 6, 27, 13, 10, 10, 250);
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+
+      let fmt = new DateTimeFormat(DateTimePatterns_de.YEAR_MONTH_SHORT);
+      assertEquals('07.2006', fmt.format(date));
+      fmt = new DateTimeFormat(DateTimePatterns_de.YEAR_MONTH_ABBR);
+      assertEquals('Juli 2006', fmt.format(date));
+    }
   },
 
   testPatternDayOfWeekMonthDayMedium() {
-    date = new Date(2006, 6, 27, 13, 10, 10, 250);
-
-    let fmt =
-        new DateTimeFormat(goog.i18n.DateTimePatterns.WEEKDAY_MONTH_DAY_MEDIUM);
-    assertEquals('Thu, Jul 27', fmt.format(date));
-
-    goog.i18n.DateTimePatterns = DateTimePatterns_de;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_de;
-    fmt =
-        new DateTimeFormat(goog.i18n.DateTimePatterns.WEEKDAY_MONTH_DAY_MEDIUM);
-    assertEquals('Do., 27. Juli', fmt.format(date));
+    const date = new Date(2006, 6, 27, 13, 10, 10, 250);
+
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+
+      replacer.replace(goog, 'LOCALE', 'en');
+      replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_en);
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_en);
+      let fmt = new DateTimeFormat(DateTimePatterns.WEEKDAY_MONTH_DAY_MEDIUM);
+      assertEquals('Thu, Jul 27', fmt.format(date));
+
+      replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_de);
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_de);
+      replacer.replace(goog, 'LOCALE', 'de');
+      fmt = new DateTimeFormat(DateTimePatterns_de.WEEKDAY_MONTH_DAY_MEDIUM);
+      assertEquals('Do., 27. Juli', fmt.format(date));
+    }
   },
 
   testPatternDayOfWeekMonthDayYearMedium() {
-    date = new Date(2012, 5, 28, 13, 10, 10, 250);
-
-    let fmt = new DateTimeFormat(
-        goog.i18n.DateTimePatterns.WEEKDAY_MONTH_DAY_YEAR_MEDIUM);
-    assertEquals('Thu, Jun 28, 2012', fmt.format(date));
-    fmt = new DateTimeFormat(goog.i18n.DateTimePatterns.MONTH_DAY_YEAR_MEDIUM);
-    assertEquals('Jun 28, 2012', fmt.format(date));
+    const date = new Date(2012, 5, 28, 13, 10, 10, 250);
 
-    goog.i18n.DateTimePatterns = DateTimePatterns_sv;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_sv;
-    fmt = new DateTimeFormat(
-        goog.i18n.DateTimePatterns.WEEKDAY_MONTH_DAY_YEAR_MEDIUM);
-    assertEquals('tors 28 juni 2012', fmt.format(date));
-    fmt = new DateTimeFormat(goog.i18n.DateTimePatterns.MONTH_DAY_YEAR_MEDIUM);
-    assertEquals('28 juni 2012', fmt.format(date));
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+
+      replacer.replace(goog, 'LOCALE', 'en');
+      replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_en);
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_en);
+      let fmt =
+          new DateTimeFormat(DateTimePatterns_en.WEEKDAY_MONTH_DAY_YEAR_MEDIUM);
+      assertEquals('Thu, Jun 28, 2012', fmt.format(date));
+      fmt = new DateTimeFormat(DateTimePatterns_en.MONTH_DAY_YEAR_MEDIUM);
+      assertEquals('Jun 28, 2012', fmt.format(date));
+
+      replacer.replace(goog, 'LOCALE', 'sv');
+      replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_sv);
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_sv);
+      fmt = new DateTimeFormat(DateTimePatterns.WEEKDAY_MONTH_DAY_YEAR_MEDIUM);
+      assertEquals('tors, juni 28, 2012', fmt.format(date));
+      fmt = new DateTimeFormat(DateTimePatterns.MONTH_DAY_YEAR_MEDIUM);
+      assertEquals('juni 28, 2012', fmt.format(date));
+    }
   },
 
   testMonthDayHourMinuteTimezone() {
-    // Include various locales.
-    const date = new Date(2012, 5, 28, 13, 10, 10, 250);
-    const fmt = new DateTimeFormat(
-        goog.i18n.DateTimePatterns.MONTH_DAY_TIME_ZONE_SHORT);
-    assertEquals('Jun 28, 1:10 PM UTC-7', fmt.format(date));
-
-    goog.i18n.DateTimePatterns = DateTimePatterns_sv;
-    const fmtSv = new DateTimeFormat(
-        goog.i18n.DateTimePatterns.MONTH_DAY_TIME_ZONE_SHORT);
-    assertEquals('28 Jun 13:10 UTC-7', fmtSv.format(date));
-
-    goog.i18n.DateTimePatterns = DateTimePatterns_bg;
-    const fmtBg = new DateTimeFormat(
-        goog.i18n.DateTimePatterns.MONTH_DAY_TIME_ZONE_SHORT);
-    assertEquals('28.06, 13:10 ч. UTC-7', fmtBg.format(date));
-
-    goog.i18n.DateTimePatterns = DateTimePatterns_zh_HK;
-    const fmtZhHk = new DateTimeFormat(
-        goog.i18n.DateTimePatterns.MONTH_DAY_TIME_ZONE_SHORT);
-    assertEquals('6月28日 PM1:10 [UTC-7]', fmtZhHk.format(date));
-
-    // And with explicit timezone.
-    const timeZone = TimeZone.createTimeZone(-600);
-    assertEquals('6月29日 AM6:10 [UTC+10]', fmtZhHk.format(date, timeZone));
-
-    // And some from the extended patterns.
-    /** @suppress {checkTypes} suppression added to enable type checking */
-    goog.i18n.DateTimePatterns = DateTimePatterns_en_XA;
-    const fmtEnXa = new DateTimeFormat(
-        goog.i18n.DateTimePatterns.MONTH_DAY_TIME_ZONE_SHORT);
-    assertEquals(
-        '[[Jun 28 one], [13:10 UTC-7 one two] one two]', fmtEnXa.format(date));
-
-    /** @suppress {checkTypes} suppression added to enable type checking */
-    goog.i18n.DateTimePatterns = DateTimePatterns_zh_Hant_TW;
-    const fmtZhHantTw = new DateTimeFormat(
-        goog.i18n.DateTimePatterns.MONTH_DAY_TIME_ZONE_SHORT);
-    assertEquals('6月28日 PM1:10 [UTC-7]', fmtZhHantTw.format(date));
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+
+      // Include various locales.
+      replacer.replace(goog, 'LOCALE', 'en-US');
+      replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_en);
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_en);
+      const date = new Date(2012, 5, 28, 13, 10, 10, 250);
+      const fmt =
+          new DateTimeFormat(DateTimePatterns.MONTH_DAY_TIME_ZONE_SHORT);
+      assertEquals('Jun 28, 1:10 PM UTC-7', fmt.format(date));
+
+      replacer.replace(goog, 'LOCALE', 'sv');
+      replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_sv);
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_sv);
+      const fmtSv =
+          new DateTimeFormat(DateTimePatterns_sv.MONTH_DAY_TIME_ZONE_SHORT);
+      assertEquals('28 juni 13:10 UTC-7', fmtSv.format(date));
+
+      replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_bg);
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_bg);
+      replacer.replace(goog, 'LOCALE', 'bg');
+      const fmtBg =
+          new DateTimeFormat(DateTimePatterns_bg.MONTH_DAY_TIME_ZONE_SHORT);
+      assertEquals('28.06, 13:10 ч. UTC-7', fmtBg.format(date));
+
+      replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_zh_HK);
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_zh_HK);
+      replacer.replace(goog, 'LOCALE', 'zh_HK');
+      const fmtZhHk =
+          new DateTimeFormat(DateTimePatterns_zh_HK.MONTH_DAY_TIME_ZONE_SHORT);
+      assertEquals('6月28日 下午1:10 [UTC-7]', fmtZhHk.format(date));
+
+      // And with explicit timezone.
+      const timeZone = TimeZone.createTimeZone(-600);
+      assertEquals('6月29日 上午6:10 [UTC+10]', fmtZhHk.format(date, timeZone));
+
+      // And some from the extended patterns.
+      replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_en_XA);
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_en_XA);
+      replacer.replace(goog, 'LOCALE', 'en_XA');
+      const fmtEnXa = new DateTimeFormat(
+          goog.i18n.DateTimePatterns.MONTH_DAY_TIME_ZONE_SHORT);
+      assertEquals(
+          '[[[Ĵûñ one] 28 one], [13:10 UTC-7 one two] one two]',
+          fmtEnXa.format(date));
+
+      replacer.replace(
+          goog.i18n, 'DateTimePatterns', DateTimePatterns_zh_Hant_TW);
+      replacer.replace(
+          goog.i18n, 'DateTimeSymbols', DateTimeSymbols_zh_Hant_TW);
+      replacer.replace(goog, 'LOCALE', 'zh_Hant_TW');
+      const fmtZhHantTw = new DateTimeFormat(
+          goog.i18n.DateTimePatterns.MONTH_DAY_TIME_ZONE_SHORT);
+      assertEquals('6月28日 下午1:10 [UTC-7]', fmtZhHantTw.format(date));
+    }
   },
 
   testQuote() {
-    goog.i18n.DateTimePatterns = DateTimePatterns_de;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_de;
-    date = new Date(2006, 6, 27, 13, 10, 10, 250);
-    let fmt = new DateTimeFormat('HH \'o\'\'clock\'');
-    assertEquals('13 o\'clock', fmt.format(date));
-    fmt = new DateTimeFormat('HH \'oclock\'');
-    assertEquals('13 oclock', fmt.format(date));
-    fmt = new DateTimeFormat('HH \'\'');
-    assertEquals('13 \'', fmt.format(date));
+    const date = new Date(2006, 6, 27, 13, 10, 10, 250);
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+      replacer.replace(goog, 'LOCALE', 'de');
+      replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_de);
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_de);
+
+      let fmt = new DateTimeFormat('HH \'o\'\'clock\'');
+      assertEquals('13 o\'clock', fmt.format(date));
+      fmt = new DateTimeFormat('HH \'oclock\'');
+      assertEquals('13 oclock', fmt.format(date));
+      fmt = new DateTimeFormat('HH \'\'');
+      assertEquals('13 \'', fmt.format(date));
+    }
   },
 
   testFractionalSeconds() {
-    goog.i18n.DateTimePatterns = DateTimePatterns_de;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_de;
-    date = new Date(2006, 6, 27, 13, 10, 10, 256);
-    let fmt = new DateTimeFormat('s:S');
-    assertEquals('10:3', fmt.format(date));
-    fmt = new DateTimeFormat('s:SS');
-    assertEquals('10:26', fmt.format(date));
-    fmt = new DateTimeFormat('s:SSS');
-    assertEquals('10:256', fmt.format(date));
-    fmt = new DateTimeFormat('s:SSSS');
-    assertEquals('10:2560', fmt.format(date));
-    fmt = new DateTimeFormat('s:SSSSS');
-    assertEquals('10:25600', fmt.format(date));
-
-    date = new Date(1960, 6, 27, 13, 10, 10, 256);
-    fmt = new DateTimeFormat('s:S');
-    assertEquals('10:3', fmt.format(date));
-    fmt = new DateTimeFormat('s:SS');
-    assertEquals('10:26', fmt.format(date));
-    fmt = new DateTimeFormat('s:SSS');
-    assertEquals('10:256', fmt.format(date));
-    fmt = new DateTimeFormat('s:SSSS');
-    assertEquals('10:2560', fmt.format(date));
-    fmt = new DateTimeFormat('s:SSSSS');
-    assertEquals('10:25600', fmt.format(date));
+    for (let nativeMode of testECMAScriptOptions) {
+      let date = new Date(2006, 6, 27, 13, 10, 10, 256);
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+      replacer.replace(goog, 'LOCALE', 'de');
+      replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_de);
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_de);
+
+      let fmt = new DateTimeFormat('s:S');
+      assertEquals('10:3', fmt.format(date));
+      fmt = new DateTimeFormat('s:SS');
+      assertEquals('10:26', fmt.format(date));
+      fmt = new DateTimeFormat('s:SSS');
+      assertEquals('10:256', fmt.format(date));
+      fmt = new DateTimeFormat('s:SSSS');
+      assertEquals('10:2560', fmt.format(date));
+      fmt = new DateTimeFormat('s:SSSSS');
+      assertEquals('10:25600', fmt.format(date));
+
+      date = new Date(1960, 6, 27, 13, 10, 10, 256);
+      fmt = new DateTimeFormat('s:S');
+      assertEquals('10:3', fmt.format(date));
+      fmt = new DateTimeFormat('s:SS');
+      assertEquals('10:26', fmt.format(date));
+      fmt = new DateTimeFormat('s:SSS');
+      assertEquals('10:256', fmt.format(date));
+      fmt = new DateTimeFormat('s:SSSS');
+      assertEquals('10:2560', fmt.format(date));
+      fmt = new DateTimeFormat('s:SSSSS');
+      assertEquals('10:25600', fmt.format(date));
+    }
   },
 
   /** @suppress {checkTypes} suppression added to enable type checking */
   testPredefinedFormatter() {
-    goog.i18n.DateTimePatterns = DateTimePatterns_de;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_de;
-    date = new Date(2006, 7, 4, 13, 49, 24, 0);
-    let fmt = new DateTimeFormat(DateTimeFormat.Format.FULL_DATE);
-    assertEquals('Freitag, 4. August 2006', fmt.format(date));
-    fmt = new DateTimeFormat(DateTimeFormat.Format.LONG_DATE);
-    assertEquals('4. August 2006', fmt.format(date));
-    fmt = new DateTimeFormat(DateTimeFormat.Format.MEDIUM_DATE);
-    assertEquals('04.08.2006', fmt.format(date));
-    fmt = new DateTimeFormat(DateTimeFormat.Format.SHORT_DATE);
-    assertEquals('04.08.06', fmt.format(date));
-    fmt = new DateTimeFormat(DateTimeFormat.Format.FULL_TIME);
-    assertEquals('13:49:24 ' + timezoneString(date), fmt.format(date));
-    fmt = new DateTimeFormat(DateTimeFormat.Format.LONG_TIME);
-    assertEquals('13:49:24 ' + timezoneString(date), fmt.format(date));
-    fmt = new DateTimeFormat(DateTimeFormat.Format.MEDIUM_TIME);
-    assertEquals('13:49:24', fmt.format(date));
-    fmt = new DateTimeFormat(DateTimeFormat.Format.SHORT_TIME);
-    assertEquals('13:49', fmt.format(date));
-    fmt = new DateTimeFormat(DateTimeFormat.Format.FULL_DATETIME);
-    assertEquals(
-        'Freitag, 4. August 2006 um 13:49:24 ' + timezoneString(date),
-        fmt.format(date));
-    fmt = new DateTimeFormat(DateTimeFormat.Format.LONG_DATETIME);
-    assertEquals(
-        '4. August 2006 um 13:49:24 ' + timezoneString(date), fmt.format(date));
-    fmt = new DateTimeFormat(DateTimeFormat.Format.MEDIUM_DATETIME);
-    assertEquals('04.08.2006, 13:49:24', fmt.format(date));
-    fmt = new DateTimeFormat(DateTimeFormat.Format.SHORT_DATETIME);
-    assertEquals('04.08.06, 13:49', fmt.format(date));
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+      replacer.replace(goog, 'LOCALE', 'de');
+
+      replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_de);
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_de);
+      const date = new Date(2006, 7, 4, 13, 49, 24, 0);
+
+      let fmt = new DateTimeFormat(DateTimeFormat.Format.FULL_DATE);
+      let result = removeLtrMarkers(fmt.format(date));
+      assertEquals('Freitag, 4. August 2006', result);
+
+      fmt = new DateTimeFormat(DateTimeFormat.Format.LONG_DATE);
+      result = removeLtrMarkers(fmt.format(date));
+      assertEquals('4. August 2006', result);
+
+      fmt = new DateTimeFormat(DateTimeFormat.Format.MEDIUM_DATE);
+      result = removeLtrMarkers(fmt.format(date));
+      assertEquals('nativeMode = ' + nativeMode, '04.08.2006', result);
+
+      fmt = new DateTimeFormat(DateTimeFormat.Format.SHORT_DATE);
+      result = removeLtrMarkers(fmt.format(date));
+      let expected = '04.08.06';
+      assertEquals(expected, result);
+
+      fmt = new DateTimeFormat(DateTimeFormat.Format.FULL_TIME);
+      result = fmt.format(date);
+
+      // This timezone result does not change with the type of time (FULL..SHORT).
+      let timezoneResult = timezoneString(date);
+      const theTime = '13:49:24';
+      expected = theTime + ' ' + timezoneResult;
+
+      if (nativeMode) {
+        const expected2 = theTime + ' Nordamerikanische Westküsten-Sommerzeit';
+        assertEquals('nativeMode = ' + nativeMode,
+                     expected2, result);
+      } else {
+        assertEquals(expected, result);
+      }
+
+      fmt = new DateTimeFormat(DateTimeFormat.Format.LONG_TIME);
+      result = fmt.format(date);
+      assertEquals('nativeMode = ' + nativeMode, expected, result);
+
+      fmt = new DateTimeFormat(DateTimeFormat.Format.MEDIUM_TIME);
+      result = removeLtrMarkers(fmt.format(date));
+      assertEquals('nativeMode = ' + nativeMode, theTime, result);
+
+      fmt = new DateTimeFormat(DateTimeFormat.Format.SHORT_TIME);
+      result = removeLtrMarkers(fmt.format(date));
+      assertEquals('13:49', result);
+
+      fmt = new DateTimeFormat(DateTimeFormat.Format.FULL_DATETIME);
+      result = removeDirectionMarkers(fmt.format(date));
+      expected = nativeMode ?
+          'Freitag, 4. August 2006 um 13:49:24 Nordamerikanische Westküsten-Sommerzeit' :
+          'Freitag, 4. August 2006 um 13:49:24 UTC-7';
+      // TODO(user): Resolve timezone full name
+      assertEquals('nativeMode=' + nativeMode, expected, result);
+
+      fmt = new DateTimeFormat(DateTimeFormat.Format.LONG_DATETIME);
+      expected = '4. August 2006 um 13:49:24 ' + timezoneResult;
+      result = removeDirectionMarkers(fmt.format(date));
+      assertEquals('nativeMode=' + nativeMode, expected, result);
+
+      fmt = new DateTimeFormat(DateTimeFormat.Format.MEDIUM_DATETIME);
+      // TODO(user): Why this difference?
+      expected = '04.08.2006, 13:49:24';
+      assertEquals('nativeMode=' + nativeMode, expected, fmt.format(date));
+
+      fmt = new DateTimeFormat(DateTimeFormat.Format.SHORT_DATETIME);
+      expected = '04.08.06, 13:49';
+      assertEquals('nativeMode=' + nativeMode, expected, fmt.format(date));
+    }
   },
 
   testMMddyyyyHHmmssZSimpleTimeZone() {
-    goog.i18n.DateTimePatterns = DateTimePatterns_de;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_de;
-    const date = new Date(Date.UTC(2006, 6, 27, 13, 10, 10));
-    const timeZone = TimeZone.createTimeZone(480);
-    let fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss Z');
-    assertEquals('07/27/2006 05:10:10 -0800', fmt.format(date, timeZone));
-    fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss ZZ');
-    assertEquals('07/27/2006 05:10:10 -0800', fmt.format(date, timeZone));
-    fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss ZZZ');
-    assertEquals('07/27/2006 05:10:10 -0800', fmt.format(date, timeZone));
-    fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss ZZZZ');
-    assertEquals('07/27/2006 05:10:10 GMT-08:00', fmt.format(date, timeZone));
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+      replacer.replace(goog, 'LOCALE', 'de');
+      replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_de);
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_de);
+
+      const date = new Date(Date.UTC(2006, 6, 27, 13, 10, 10));
+      const timeZone = TimeZone.createTimeZone(480);
+      let fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss Z');
+      assertEquals('07/27/2006 05:10:10 -0800', fmt.format(date, timeZone));
+      fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss ZZ');
+      assertEquals('07/27/2006 05:10:10 -0800', fmt.format(date, timeZone));
+      fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss ZZZ');
+      assertEquals('07/27/2006 05:10:10 -0800', fmt.format(date, timeZone));
+      fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss ZZZZ');
+      assertEquals('07/27/2006 05:10:10 GMT-08:00', fmt.format(date, timeZone));
+    }
   },
 
   testMMddyyyyHHmmssZCommonTimeZone() {
-    goog.i18n.DateTimePatterns = DateTimePatterns_de;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_de;
-    let date = new Date(Date.UTC(2006, 6, 27, 13, 10, 10));
-    const timeZone = TimeZone.createTimeZone(americaLosAngelesData);
-    let fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss Z');
-    assertEquals('07/27/2006 06:10:10 -0700', fmt.format(date, timeZone));
-    fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss ZZ');
-    assertEquals('07/27/2006 06:10:10 -0700', fmt.format(date, timeZone));
-    fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss ZZZ');
-    assertEquals('07/27/2006 06:10:10 -0700', fmt.format(date, timeZone));
-    fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss ZZZZ');
-    assertEquals('07/27/2006 06:10:10 GMT-07:00', fmt.format(date, timeZone));
-    date = new Date(Date.UTC(2006, 1, 27, 13, 10, 10));
-    fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss Z');
-    assertEquals('02/27/2006 05:10:10 -0800', fmt.format(date, timeZone));
-    fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss ZZ');
-    assertEquals('02/27/2006 05:10:10 -0800', fmt.format(date, timeZone));
-    fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss ZZZ');
-    assertEquals('02/27/2006 05:10:10 -0800', fmt.format(date, timeZone));
-    fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss ZZZZ');
-    assertEquals('02/27/2006 05:10:10 GMT-08:00', fmt.format(date, timeZone));
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+      replacer.replace(goog, 'LOCALE', 'de');
+      replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_de);
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_de);
+
+      let date = new Date(Date.UTC(2006, 6, 27, 13, 10, 10));
+      const timeZone = TimeZone.createTimeZone(americaLosAngelesData);
+      let fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss Z');
+      assertEquals('07/27/2006 06:10:10 -0700', fmt.format(date, timeZone));
+      fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss ZZ');
+      assertEquals('07/27/2006 06:10:10 -0700', fmt.format(date, timeZone));
+      fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss ZZZ');
+      assertEquals('07/27/2006 06:10:10 -0700', fmt.format(date, timeZone));
+      fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss ZZZZ');
+      assertEquals('07/27/2006 06:10:10 GMT-07:00', fmt.format(date, timeZone));
+
+      date = new Date(Date.UTC(2006, 1, 27, 13, 10, 10));
+      fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss Z');
+      assertEquals('02/27/2006 05:10:10 -0800', fmt.format(date, timeZone));
+      fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss ZZ');
+      assertEquals('02/27/2006 05:10:10 -0800', fmt.format(date, timeZone));
+      fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss ZZZ');
+      assertEquals('02/27/2006 05:10:10 -0800', fmt.format(date, timeZone));
+      fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss ZZZZ');
+      assertEquals('02/27/2006 05:10:10 GMT-08:00', fmt.format(date, timeZone));
+    }
   },
 
   testMMddyyyyHHmmsszSimpleTimeZone() {
-    goog.i18n.DateTimePatterns = DateTimePatterns_de;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_de;
-    const date = new Date(Date.UTC(2006, 6, 27, 13, 10, 10));
-    const timeZone = TimeZone.createTimeZone(420);
-    let fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss z');
-    assertEquals('07/27/2006 06:10:10 UTC-7', fmt.format(date, timeZone));
-    fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss zz');
-    assertEquals('07/27/2006 06:10:10 UTC-7', fmt.format(date, timeZone));
-    fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss zzz');
-    assertEquals('07/27/2006 06:10:10 UTC-7', fmt.format(date, timeZone));
-    fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss zzzz');
-    assertEquals('07/27/2006 06:10:10 UTC-7', fmt.format(date, timeZone));
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+      replacer.replace(goog, 'LOCALE', 'de');
+      replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_de);
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_de);
+
+      const date = new Date(Date.UTC(2006, 6, 27, 13, 10, 10));
+      const timeZone = TimeZone.createTimeZone(420);
+      let fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss z');
+      assertEquals('07/27/2006 06:10:10 UTC-7', fmt.format(date, timeZone));
+      fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss zz');
+      assertEquals('07/27/2006 06:10:10 UTC-7', fmt.format(date, timeZone));
+      fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss zzz');
+      assertEquals('07/27/2006 06:10:10 UTC-7', fmt.format(date, timeZone));
+      fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss zzzz');
+      assertEquals('07/27/2006 06:10:10 UTC-7', fmt.format(date, timeZone));
+    }
   },
 
   testMMddyyyyHHmmsszCommonTimeZone() {
-    goog.i18n.DateTimePatterns = DateTimePatterns_de;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_de;
-    let date = new Date(Date.UTC(2006, 6, 27, 13, 10, 10));
-    let timeZone = TimeZone.createTimeZone(americaLosAngelesData);
-    let fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss z');
-    assertEquals('07/27/2006 06:10:10 PDT', fmt.format(date, timeZone));
-    fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss zz');
-    assertEquals('07/27/2006 06:10:10 PDT', fmt.format(date, timeZone));
-    fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss zzz');
-    assertEquals('07/27/2006 06:10:10 PDT', fmt.format(date, timeZone));
-    fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss zzzz');
-    assertEquals(
-        '07/27/2006 06:10:10 Pacific Daylight Time',
-        fmt.format(date, timeZone));
-    date = new Date(Date.UTC(2006, 1, 27, 13, 10, 10));
-    fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss z');
-    assertEquals('02/27/2006 05:10:10 PST', fmt.format(date, timeZone));
-    fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss zz');
-    assertEquals('02/27/2006 05:10:10 PST', fmt.format(date, timeZone));
-    fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss zzz');
-    assertEquals('02/27/2006 05:10:10 PST', fmt.format(date, timeZone));
-    fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss zzzz');
-    assertEquals(
-        '02/27/2006 05:10:10 Pacific Standard Time',
-        fmt.format(date, timeZone));
-
-    timeZone = TimeZone.createTimeZone(europeBerlinData);
-    fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss z');
-    assertEquals('02/27/2006 14:10:10 MEZ', fmt.format(date, timeZone));
-    fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss zzzz');
-    assertEquals(
-        '02/27/2006 14:10:10 Mitteleurop\u00e4ische Zeit',
-        fmt.format(date, timeZone));
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+      replacer.replace(goog, 'LOCALE', 'de');
+      replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_de);
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_de);
+
+      let date = new Date(Date.UTC(2006, 6, 27, 13, 10, 10));
+      let timeZone = TimeZone.createTimeZone(americaLosAngelesData);
+      let fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss z');
+      assertEquals('07/27/2006 06:10:10 PDT', fmt.format(date, timeZone));
+      fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss zz');
+      assertEquals('07/27/2006 06:10:10 PDT', fmt.format(date, timeZone));
+      fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss zzz');
+      assertEquals('07/27/2006 06:10:10 PDT', fmt.format(date, timeZone));
+      fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss zzzz');
+      assertEquals(
+          '07/27/2006 06:10:10 Pacific Daylight Time',
+          fmt.format(date, timeZone));
+      date = new Date(Date.UTC(2006, 1, 27, 13, 10, 10));
+      fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss z');
+      assertEquals('02/27/2006 05:10:10 PST', fmt.format(date, timeZone));
+      fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss zz');
+      assertEquals('02/27/2006 05:10:10 PST', fmt.format(date, timeZone));
+      fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss zzz');
+      assertEquals('02/27/2006 05:10:10 PST', fmt.format(date, timeZone));
+      fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss zzzz');
+      assertEquals(
+          '02/27/2006 05:10:10 Pacific Standard Time',
+          fmt.format(date, timeZone));
+
+      timeZone = TimeZone.createTimeZone(europeBerlinData);
+      fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss z');
+      assertEquals('02/27/2006 14:10:10 MEZ', fmt.format(date, timeZone));
+      fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss zzzz');
+      assertEquals(
+          '02/27/2006 14:10:10 Mitteleurop\u00e4ische Zeit',
+          fmt.format(date, timeZone));
+    }
   },
 
   testMMddyyyyHHmmssvCommonTimeZone() {
-    goog.i18n.DateTimePatterns = DateTimePatterns_de;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_de;
-    const date = new Date(Date.UTC(2006, 6, 27, 13, 10, 10));
-    const timeZone = TimeZone.createTimeZone(americaLosAngelesData);
-    let fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss v');
-    assertEquals(
-        '07/27/2006 06:10:10 America/Los_Angeles', fmt.format(date, timeZone));
-    fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss vv');
-    assertEquals(
-        '07/27/2006 06:10:10 America/Los_Angeles', fmt.format(date, timeZone));
-    fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss vvv');
-    assertEquals(
-        '07/27/2006 06:10:10 America/Los_Angeles', fmt.format(date, timeZone));
-    fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss vvvv');
-    assertEquals(
-        '07/27/2006 06:10:10 America/Los_Angeles', fmt.format(date, timeZone));
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+      replacer.replace(goog, 'LOCALE', 'de');
+      replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_de);
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_de);
+
+      const date = new Date(Date.UTC(2006, 6, 27, 13, 10, 10));
+      const timeZone = TimeZone.createTimeZone(americaLosAngelesData);
+      let fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss v');
+      assertEquals(
+          '07/27/2006 06:10:10 America/Los_Angeles',
+          fmt.format(date, timeZone));
+      fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss vv');
+      assertEquals(
+          '07/27/2006 06:10:10 America/Los_Angeles',
+          fmt.format(date, timeZone));
+      fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss vvv');
+      assertEquals(
+          '07/27/2006 06:10:10 America/Los_Angeles',
+          fmt.format(date, timeZone));
+      fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss vvvv');
+      assertEquals(
+          '07/27/2006 06:10:10 America/Los_Angeles',
+          fmt.format(date, timeZone));
+    }
   },
 
   testMMddyyyyHHmmssvSimpleTimeZone() {
-    goog.i18n.DateTimePatterns = DateTimePatterns_de;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_de;
-    const date = new Date(Date.UTC(2006, 6, 27, 13, 10, 10));
-    const timeZone = TimeZone.createTimeZone(420);
-    let fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss v');
-    assertEquals('07/27/2006 06:10:10 Etc/GMT+7', fmt.format(date, timeZone));
-    fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss vv');
-    assertEquals('07/27/2006 06:10:10 Etc/GMT+7', fmt.format(date, timeZone));
-    fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss vvv');
-    assertEquals('07/27/2006 06:10:10 Etc/GMT+7', fmt.format(date, timeZone));
-    fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss vvvv');
-    assertEquals('07/27/2006 06:10:10 Etc/GMT+7', fmt.format(date, timeZone));
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+      replacer.replace(goog, 'LOCALE', 'de');
+      replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_de);
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_de);
+
+      const date = new Date(Date.UTC(2006, 6, 27, 13, 10, 10));
+      const timeZone = TimeZone.createTimeZone(420);
+      let fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss v');
+      assertEquals('07/27/2006 06:10:10 Etc/GMT+7', fmt.format(date, timeZone));
+      fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss vv');
+      assertEquals('07/27/2006 06:10:10 Etc/GMT+7', fmt.format(date, timeZone));
+      fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss vvv');
+      assertEquals('07/27/2006 06:10:10 Etc/GMT+7', fmt.format(date, timeZone));
+      fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss vvvv');
+      assertEquals('07/27/2006 06:10:10 Etc/GMT+7', fmt.format(date, timeZone));
+    }
   },
 
   testMMddyyyyHHmmssVCommonTimeZone() {
-    goog.i18n.DateTimePatterns = DateTimePatterns_de;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_de;
-    const date = new Date(Date.UTC(2006, 6, 27, 13, 10, 10));
-    const timeZone = TimeZone.createTimeZone(americaLosAngelesData);
-    let fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss V');
-    assertEquals(
-        '07/27/2006 06:10:10 America/Los_Angeles', fmt.format(date, timeZone));
-    fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss VV');
-    assertEquals(
-        '07/27/2006 06:10:10 America/Los_Angeles', fmt.format(date, timeZone));
-    fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss VVV');
-    assertEquals(
-        '07/27/2006 06:10:10 Los Angeles Time', fmt.format(date, timeZone));
-    fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss VVVV');
-    assertEquals(
-        '07/27/2006 06:10:10 Los Angeles Time', fmt.format(date, timeZone));
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+      replacer.replace(goog, 'LOCALE', 'de');
+      replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_de);
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_de);
+
+      const date = new Date(Date.UTC(2006, 6, 27, 13, 10, 10));
+      const timeZone = TimeZone.createTimeZone(americaLosAngelesData);
+      let fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss V');
+      assertEquals(
+          '07/27/2006 06:10:10 America/Los_Angeles',
+          fmt.format(date, timeZone));
+      fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss VV');
+      assertEquals(
+          '07/27/2006 06:10:10 America/Los_Angeles',
+          fmt.format(date, timeZone));
+      fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss VVV');
+      assertEquals(
+          '07/27/2006 06:10:10 Los Angeles Time', fmt.format(date, timeZone));
+      fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss VVVV');
+      assertEquals(
+          '07/27/2006 06:10:10 Los Angeles Time', fmt.format(date, timeZone));
+    }
   },
 
   testMMddyyyyHHmmssVSimpleTimeZone() {
-    goog.i18n.DateTimePatterns = DateTimePatterns_de;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_de;
-    const date = new Date(Date.UTC(2006, 6, 27, 13, 10, 10));
-    const timeZone = TimeZone.createTimeZone(420);
-    let fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss V');
-    assertEquals('07/27/2006 06:10:10 Etc/GMT+7', fmt.format(date, timeZone));
-    fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss VV');
-    assertEquals('07/27/2006 06:10:10 Etc/GMT+7', fmt.format(date, timeZone));
-    fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss VVV');
-    assertEquals('07/27/2006 06:10:10 GMT-07:00', fmt.format(date, timeZone));
-    fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss VVVV');
-    assertEquals('07/27/2006 06:10:10 GMT-07:00', fmt.format(date, timeZone));
+    replacer.replace(goog, 'LOCALE', 'de');
+    replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_de);
+    replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_de);
+
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+      const date = new Date(Date.UTC(2006, 6, 27, 13, 10, 10));
+      const timeZone = TimeZone.createTimeZone(420);
+      let fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss V');
+      assertEquals('07/27/2006 06:10:10 Etc/GMT+7', fmt.format(date, timeZone));
+      fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss VV');
+      assertEquals('07/27/2006 06:10:10 Etc/GMT+7', fmt.format(date, timeZone));
+      fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss VVV');
+      assertEquals('07/27/2006 06:10:10 GMT-07:00', fmt.format(date, timeZone));
+      fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss VVVV');
+      assertEquals('07/27/2006 06:10:10 GMT-07:00', fmt.format(date, timeZone));
+    }
   },
 
   test_yyyyMMddG() {
-    goog.i18n.DateTimePatterns = DateTimePatterns_de;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_de;
+    replacer.replace(goog, 'LOCALE', 'de');
+    replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_de);
+    replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_de);
+
     const date = new Date(Date.UTC(2006, 6, 27, 20, 10, 10));
-    let timeZone = TimeZone.createTimeZone(420);
-    let fmt = new DateTimeFormat('yyyy.MM.dd G \'at\' HH:mm:ss vvvv');
-    assertEquals(
-        '2006.07.27 n. Chr. at 13:10:10 Etc/GMT+7', fmt.format(date, timeZone));
 
-    timeZone = TimeZone.createTimeZone(americaLosAngelesData);
-    fmt = new DateTimeFormat('yyyy.MM.dd G \'at\' HH:mm:ss vvvv');
-    assertEquals(
-        '2006.07.27 n. Chr. at 13:10:10 America/Los_Angeles',
-        fmt.format(date, timeZone));
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+      let timeZone = TimeZone.createTimeZone(420);
+      let fmt = new DateTimeFormat('yyyy.MM.dd G \'at\' HH:mm:ss vvvv');
+      assertEquals(
+          '2006.07.27 n. Chr. at 13:10:10 Etc/GMT+7',
+          fmt.format(date, timeZone));
+
+      timeZone = TimeZone.createTimeZone(americaLosAngelesData);
+      fmt = new DateTimeFormat('yyyy.MM.dd G \'at\' HH:mm:ss vvvv');
+      assertEquals(
+          '2006.07.27 n. Chr. at 13:10:10 America/Los_Angeles',
+          fmt.format(date, timeZone));
+    }
   },
 
   test_daylightTimeTransition() {
-    goog.i18n.DateTimePatterns = DateTimePatterns_de;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_de;
+    replacer.replace(goog, 'LOCALE', 'de');
+    replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_de);
+    replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_de);
 
     // US PST transition to PDT on 2006/4/2/ 2:00am, jump to 2006/4/2 3:00am,
     // That's UTC time 2006/4/2 10:00am
@@ -684,283 +979,455 @@ testSuite({
   },
 
   test_timeDisplayOnDaylighTimeTransition() {
-    goog.i18n.DateTimePatterns = DateTimePatterns_de;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_de;
-
-    // US PST transition to PDT on 2006/4/2/ 2:00am, jump to 2006/4/2 3:00am,
-    let date = new Date(Date.UTC(2006, 4 - 1, 2, 2, 30, 0));
-    const timeZone = TimeZone.createTimeZone(0);
-    let fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss Z');
-    assertEquals('04/02/2006 02:30:00 +0000', fmt.format(date, timeZone));
-
-    // US PDT transition to PST on 2006/10/29/ 2:00am, jump back to PDT
-    // 2006/4/2 1:00am,
-    date = new Date(Date.UTC(2006, 10 - 1, 29, 1, 30, 0));
-    fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss Z');
-    assertEquals('10/29/2006 01:30:00 +0000', fmt.format(date, timeZone));
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+      replacer.replace(goog, 'LOCALE', 'de');
+      replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_de);
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_de);
+
+      // US PST transition to PDT on 2006/4/2/ 2:00am, jump to 2006/4/2 3:00am,
+      let date = new Date(Date.UTC(2006, 4 - 1, 2, 2, 30, 0));
+      const timeZone = TimeZone.createTimeZone(0);
+      let fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss Z');
+      assertEquals('04/02/2006 02:30:00 +0000', fmt.format(date, timeZone));
+
+      // US PDT transition to PST on 2006/10/29/ 2:00am, jump back to PDT
+      // 2006/4/2 1:00am,
+      date = new Date(Date.UTC(2006, 10 - 1, 29, 1, 30, 0));
+      fmt = new DateTimeFormat('MM/dd/yyyy HH:mm:ss Z');
+      assertEquals('10/29/2006 01:30:00 +0000', fmt.format(date, timeZone));
+    }
   },
 
   testTimeDisplayOnDaylightTimeTransitionDayChange() {
     // NOTE: this test is a regression test only if the test browser has an OS
     // timezone of PST. While the test should still work in other timezones, it
     // does not serve as a regression test in them.
-    goog.i18n.DateTimePatterns = DateTimePatterns_de;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_de;
-
-    // Time is 2015/11/01 3:00:01am after US PDT -> PST. 11:00:01am UTC.
-    const date = new Date(Date.UTC(2015, 11 - 1, 1, 11, 0, 1));
-    // Convert to GMT-12, across DST transition.
-    // The date should also change, but does not change when subtracting 4 hours
-    // from PST/PDT due to the extra hour from switching DST.
-    const timeZone = TimeZone.createTimeZone(12 * 60);
-    const fmt = new DateTimeFormat('yyyy/MM/dd HH:mm:ss Z');
-    // Regression test: this once returned 2015/11/01 instead.
-    assertEquals('2015/10/31 23:00:01 -1200', fmt.format(date, timeZone));
+    replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_de);
+    replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_de);
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+
+      replacer.replace(goog, 'LOCALE', 'de');
+
+      // Time is 2015/11/01 3:00:01am after US PDT -> PST. 11:00:01am UTC.
+      const date = new Date(Date.UTC(2015, 11 - 1, 1, 11, 0, 1));
+      // Convert to GMT-12, across DST transition.
+      // The date should also change, but does not change when subtracting 4
+      // hours from PST/PDT due to the extra hour from switching DST.
+      const timeZone = TimeZone.createTimeZone(12 * 60);
+      const fmt = new DateTimeFormat('yyyy/MM/dd HH:mm:ss Z');
+      // Regression test: this once returned 2015/11/01 instead.
+      assertEquals('2015/10/31 23:00:01 -1200', fmt.format(date, timeZone));
+    }
   },
 
   test_nativeDigits_fa() {
-    goog.i18n.DateTimePatterns = DateTimePatterns_fa;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_fa;
-
-    date = new Date(2006, 7 - 1, 27, 13, 10, 10, 250);
-    const timeZone = TimeZone.createTimeZone(420);
-    let fmt = new DateTimeFormat('y/MM/dd H:mm:ss٫SS');
-    assertEquals('۲۰۰۶/۰۷/۲۷ ۱۳:۱۰:۱۰٫۲۵', fmt.format(date));
-
-    // Make sure standardized timezone formats don't use native digits
-    fmt = new DateTimeFormat('Z');
-    assertEquals('-0700', fmt.format(date, timeZone));
+    const date = new Date(2006, 7 - 1, 27, 13, 10, 10, 250);
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+      replacer.replace(goog, 'LOCALE', 'fa');
+      replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_fa);
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_fa);
+
+      const timeZone = TimeZone.createTimeZone(420);
+      let fmt = new DateTimeFormat('y/MM/dd H:mm:ss٫SS');
+      assertEquals('۲۰۰۶/۰۷/۲۷ ۱۳:۱۰:۱۰٫۲۵', fmt.format(date));
+
+      // Make sure standardized timezone formats don't use native digits
+      fmt = new DateTimeFormat('Z');
+      assertEquals('-0700', fmt.format(date, timeZone));
+    }
   },
 
   test_nativeDigits_ar() {
-    goog.i18n.DateTimePatterns = DateTimePatterns_ar_EG;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_ar_EG;
-
-    date = new Date(2006, 7 - 1, 27, 13, 10, 10, 250);
-    const timeZone = TimeZone.createTimeZone(420);
-    let fmt = new DateTimeFormat('y/MM/dd H:mm:ss٫SS');
-    assertEquals('٢٠٠٦/٠٧/٢٧ ١٣:١٠:١٠٫٢٥', fmt.format(date));
-
-    fmt = new DateTimeFormat(11);
-    assertEquals('٢٧\u200f/٧\u200f/٢٠٠٦, ١:١٠ م', fmt.format(date));
-
-    // Make sure standardized timezone formats don't use native digits
-    fmt = new DateTimeFormat('Z');
-    assertEquals('-0700', fmt.format(date, timeZone));
+    const date = new Date(2006, 7 - 1, 27, 13, 10, 10, 250);
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+      replacer.replace(goog, 'LOCALE', 'ar_EG');
+      replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_ar_EG);
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_ar_EG);
+
+      const timeZone = TimeZone.createTimeZone(420);
+      let fmt = new DateTimeFormat('y/MM/dd H:mm:ss٫SS');
+      assertEquals('٢٠٠٦/٠٧/٢٧ ١٣:١٠:١٠٫٢٥', fmt.format(date));
+
+      fmt = new DateTimeFormat(11);
+      let result = fmt.format(date);
+      const hasAsciiDigit = /[0-9]/.test(result);
+      assertFalse('No ASCII digits = ' + result, hasAsciiDigit);
+
+      // Make sure standardized timezone formats don't use native digits
+      fmt = new DateTimeFormat('Z');
+      assertEquals('-0700', fmt.format(date, timeZone));
+    }
   },
 
   test_enforceAsciiDigits_ar() {
-    goog.i18n.DateTimePatterns = DateTimePatterns_ar_EG;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_ar_EG;
-
-    DateTimeFormat.setEnforceAsciiDigits(true);
-    date = new Date(2006, 7 - 1, 27, 13, 10, 10, 250);
-    const timeZone = TimeZone.createTimeZone(420);
-    let fmt = new DateTimeFormat('y/MM/dd H:mm:ss٫SS');
-    assertEquals('2006/07/27 13:10:10٫25', fmt.format(date));
-
-    fmt = new DateTimeFormat(11);
-    assertEquals('27/7/2006, 1:10 م', fmt.format(date));
-
-    // Make sure standardized timezone formats don't use native digits
-    fmt = new DateTimeFormat('Z');
-    assertEquals('-0700', fmt.format(date, timeZone));
+    const date = new Date(2006, 7 - 1, 27, 13, 10, 10, 250);
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+      replacer.replace(goog, 'LOCALE', 'ar_EG');
+      replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_ar_EG);
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_ar_EG);
+
+      DateTimeFormat.setEnforceAsciiDigits(true);
+      const timeZone = TimeZone.createTimeZone(420);
+      let fmt = new DateTimeFormat('y/MM/dd H:mm:ss٫SS');
+      assertEquals('2006/07/27 13:10:10٫25', fmt.format(date));
+
+      fmt = new DateTimeFormat(DateTimeFormat.Format.SHORT_DATETIME);
+      let result = fmt.format(date);
+      const hasArabicDigit = /[\u0660-\u0669]/.test(result);
+      assertFalse('Expect only ASCII = ' + result, hasArabicDigit);
+
+      // Remove LTR, RTL markers
+      result = result.replace(/\u200e/g, '').replace(/\u200f/g, '');
+
+      // Make sure standardized timezone formats don't use native digits
+      fmt = new DateTimeFormat('Z');
+      assertEquals('-0700', fmt.format(date, timeZone));
+
+      // Check with another locale.
+      replacer.replace(goog, 'LOCALE', 'my');
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_my);
+      fmt = new DateTimeFormat(DateTimeFormat.Format.SHORT_DATETIME);
+      result = fmt.format(date);
+      const hasMyanmarDigit = /[\u1040-\u1049]/.test(result);
+      assertFalse('No Myamnar digit = ' + result, hasMyanmarDigit);
+    }
   },
 
   // Making sure that the date-time combination is not a simple concatenation
   test_dateTimeConcatenation() {
-    const date = new Date(Date.UTC(2006, 4 - 1, 2, 2, 30, 0));
-    const timeZone = TimeZone.createTimeZone(americaLosAngelesData);
-    let fmt = new DateTimeFormat(DateTimeFormat.Format.FULL_DATETIME);
-    // {1} 'at' {0}
-    assertEquals(
-        'Saturday, April 1, 2006 at 6:30:00 PM Pacific Standard Time',
-        fmt.format(date, timeZone));
-    fmt = new DateTimeFormat(DateTimeFormat.Format.LONG_DATETIME);
-    assertEquals('April 1, 2006 at 6:30:00 PM PST', fmt.format(date, timeZone));
-    // {1}, {0}
-    fmt = new DateTimeFormat(DateTimeFormat.Format.MEDIUM_DATETIME);
-    assertEquals('Apr 1, 2006, 6:30:00 PM', fmt.format(date, timeZone));
-    fmt = new DateTimeFormat(DateTimeFormat.Format.SHORT_DATETIME);
-    assertEquals('4/1/06, 6:30 PM', fmt.format(date, timeZone));
+    replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_en);
+    replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_en);
+    replacer.replace(goog, 'LOCALE', 'en');
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+
+      const date = new Date(Date.UTC(2006, 4 - 1, 2, 2, 30, 0));
+      const timeZone = TimeZone.createTimeZone(americaLosAngelesData);
+
+      let fmt = new DateTimeFormat(DateTimeFormat.Format.FULL_DATETIME);
+
+      let result = fmt.format(date, timeZone);
+      let expect =
+          'Saturday, April 1, 2006 at 6:30:00 PM Pacific Standard Time';
+
+      assertEquals('nativeMode=' + nativeMode, expect, result);
+
+      fmt = new DateTimeFormat(DateTimeFormat.Format.LONG_DATETIME);
+      result = fmt.format(date, timeZone);
+      expect = 'April 1, 2006 at 6:30:00 PM PST';
+      assertEquals(expect, result);
+
+      fmt = new DateTimeFormat(DateTimeFormat.Format.MEDIUM_DATETIME);
+      expect = 'Apr 1, 2006, 6:30:00 PM';
+      result = removeLtrMarkers(fmt.format(date, timeZone));
+      let matched =
+          /Apr 1, 2006(,| at)? 6:30:00 PM/.test(result);  // Optional comma
+      assertTrue('MEDIUM_DATETIME result = ' + result,
+                 matched);
+
+      fmt = new DateTimeFormat(DateTimeFormat.Format.SHORT_DATETIME);
+      expect = '4/1/06, 6:30 PM';
+      assertEquals(
+          'SHORT_DATETIME = ' + result, expect, fmt.format(date, timeZone));
+    }
   },
 
   testNotUsingGlobalSymbols() {
-    date = new Date(2013, 10, 15);
+    const date = new Date(2013, 10, 15);
 
-    goog.i18n.DateTimePatterns = DateTimePatterns_fr;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_fr;
-    const fmtFr = new DateTimeFormat(DateTimeFormat.Format.FULL_DATE);
 
-    goog.i18n.DateTimePatterns = DateTimePatterns_de;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_de;
-    const fmtDe = new DateTimeFormat(DateTimeFormat.Format.FULL_DATE);
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
 
-    // The two formatters should return different results (French & German)
-    assertEquals('vendredi 15 novembre 2013', fmtFr.format(date));
-    assertEquals('Freitag, 15. November 2013', fmtDe.format(date));
-  },
+      replacer.replace(goog, 'LOCALE', 'fr');
+      replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_fr);
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_fr);
+      const fmtFr = new DateTimeFormat(DateTimeFormat.Format.FULL_DATE);
 
-  testConstructorSymbols() {
-    date = new Date(2013, 10, 15);
+      replacer.replace(goog, 'LOCALE', 'de');
+      replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_de);
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_de);
+      const fmtDe = new DateTimeFormat(DateTimeFormat.Format.FULL_DATE);
 
-    const fmtFr =
-        new DateTimeFormat(DateTimeFormat.Format.FULL_DATE, DateTimeSymbols_fr);
-
-    const fmtDe =
-        new DateTimeFormat(DateTimeFormat.Format.FULL_DATE, DateTimeSymbols_de);
+      // The two formatters should return different results (French & German)
+      // Remove LTR marks if present.
+      const frResult = fmtFr.format(date).replace(/\u200c/g, '');
+      assertEquals('vendredi 15 novembre 2013', frResult);
+      const deResult = fmtDe.format(date).replace(/\u200c/g, '');
+      assertEquals('Freitag, 15. November 2013', deResult);
+    }
+  },
 
-    // The two formatters should return different results (French & German)
-    assertEquals('vendredi 15 novembre 2013', fmtFr.format(date));
-    assertEquals('Freitag, 15. November 2013', fmtDe.format(date));
+  testConstructorSymbols() {
+    const date = new Date(2013, 10, 15);
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+
+      replacer.replace(goog, 'LOCALE', 'fr');
+      const fmtFr = new DateTimeFormat(
+          DateTimeFormat.Format.FULL_DATE, DateTimeSymbols_fr);
+
+      replacer.replace(goog, 'LOCALE', 'de');
+      const fmtDe = new DateTimeFormat(
+          DateTimeFormat.Format.FULL_DATE, DateTimeSymbols_de);
+
+      // The two formatters should return different results (French & German)
+      // Remove LTR marks if present.
+      let expected = '‎vendredi 15 novembre 2013'.replace(/\u200e/g, '');
+      const frResult =
+          fmtFr.format(date).replace(/\u200c/g, '').replace(/\u200e/g, '');
+      assertEquals(expected, frResult);
+      expected = 'Freitag, 15. November 2013'.replace(/\u200e/g, '');
+      const deResult =
+          fmtDe.format(date).replace(/\u200c/g, '').replace(/\u200e/g, '');
+      assertEquals(expected, deResult);
+    }
   },
 
   testQuotedPattern() {
     // Regression test for b/29990921.
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_en;
-    date = new Date(2013, 10, 15);
-
-    // Literal apostrophe
-    let fmt = new DateTimeFormat('MMM \'\'yy');
-    assertEquals('Nov \'13', fmt.format(date));
-    // Quoted text
-    fmt = new DateTimeFormat('MMM dd\'th\' yyyy');
-    assertEquals('Nov 15th 2013', fmt.format(date));
-    // Quoted text (only opening apostrophe)
-    fmt = new DateTimeFormat('MMM dd\'th yyyy');
-    assertEquals('Nov 15th yyyy', fmt.format(date));
-    // Quoted text with literal apostrophe
-    fmt = new DateTimeFormat('MMM dd\'th\'\'\'');
-    assertEquals('Nov 15th\'', fmt.format(date));
-    // Quoted text with literal apostrophe (only opening apostrophe)
-    fmt = new DateTimeFormat('MMM dd\'th\'\'');
-    assertEquals('Nov 15th\'', fmt.format(date));
+    const date = new Date(2013, 10, 15);
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_en);
+
+      // Literal apostrophe
+      let fmt = new DateTimeFormat('MMM \'\'yy');
+      assertEquals('Nov \'13', fmt.format(date));
+      // Quoted text
+      fmt = new DateTimeFormat('MMM dd\'th\' yyyy');
+      assertEquals('Nov 15th 2013', fmt.format(date));
+      // Quoted text (only opening apostrophe)
+      fmt = new DateTimeFormat('MMM dd\'th yyyy');
+      assertEquals('Nov 15th yyyy', fmt.format(date));
+      // Quoted text with literal apostrophe
+      fmt = new DateTimeFormat('MMM dd\'th\'\'\'');
+      assertEquals('Nov 15th\'', fmt.format(date));
+      // Quoted text with literal apostrophe (only opening apostrophe)
+      fmt = new DateTimeFormat('MMM dd\'th\'\'');
+      assertEquals('Nov 15th\'', fmt.format(date));
+    }
   },
 
   testSupportForWeekInYear() {
-    const date = new Date(2013, 1, 25);
-
-    goog.i18n.DateTimePatterns = DateTimePatterns_fr;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_fr;
-    let fmt = new DateTimeFormat('\'week\' w');
-    assertEquals('week 9', fmt.format(date));
-    fmt = new DateTimeFormat('\'week\' ww');
-    assertEquals('week 09', fmt.format(date));
-
-    // Make sure it uses native digits when needed
-    goog.i18n.DateTimePatterns = DateTimePatterns_fa;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_fa;
-    fmt = new DateTimeFormat('\'week\' w');
-    assertEquals('week ۹', fmt.format(date));
-    fmt = new DateTimeFormat('\'week\' ww');
-    assertEquals('week ۰۹', fmt.format(date));
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+      const date = new Date(2013, 1, 25);
+
+      replacer.replace(goog, 'LOCALE', 'fr');
+      replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_fr);
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_fr);
+      let fmt = new DateTimeFormat('\'week\' w');
+      assertEquals('week 9', fmt.format(date));
+      fmt = new DateTimeFormat('\'week\' ww');
+      assertEquals('week 09', fmt.format(date));
+
+      // Make sure it uses native digits when needed
+      replacer.replace(goog, 'LOCALE', 'fa');
+      replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_fa);
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_fa);
+      fmt = new DateTimeFormat('\'week\' w');
+      assertEquals('week ۹', fmt.format(date));
+      fmt = new DateTimeFormat('\'week\' ww');
+      assertEquals('week ۰۹', fmt.format(date));
+    }
   },
 
   testSupportYearOfWeek() {
-    const date = new Date(2005, 0, 2);
-
-    goog.i18n.DateTimePatterns = DateTimePatterns_fr;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_fr;
-    let fmt = new DateTimeFormat('YYYY');
-    assertEquals('2004', fmt.format(date));
-    fmt = new DateTimeFormat('YY');
-    assertEquals('04', fmt.format(date));
+    replacer.replace(goog, 'LOCALE', 'fr');
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+      const date = new Date(2005, 0, 2);
+
+      replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_fr);
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_fr);
+      let fmt = new DateTimeFormat('YYYY');
+      assertEquals('2004', fmt.format(date));
+      fmt = new DateTimeFormat('YY');
+      assertEquals('04', fmt.format(date));
+    }
   },
 
   testSupportForYearAndEra() {
-    const date = new Date(2013, 1, 25);
-    let fmt = new DateTimeFormat(goog.i18n.DateTimePatterns.YEAR_FULL_WITH_ERA);
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+
+      replacer.replace(goog, 'LOCALE', 'en');
+      replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_en);
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_en);
+      const date = new Date(2013, 1, 25);
+      let fmt = new DateTimeFormat(DateTimePatterns.YEAR_FULL_WITH_ERA);
 
-    assertEquals('2013 AD', fmt.format(date));
+      assertEquals('2013 AD', fmt.format(date));
 
-    date.setFullYear(213);
-    assertEquals('213 AD', fmt.format(date));
+      date.setFullYear(213);
+      assertEquals('213 AD', fmt.format(date));
 
-    date.setFullYear(11);
-    assertEquals('11 AD', fmt.format(date));
+      date.setFullYear(11);
+      assertEquals('11 AD', fmt.format(date));
 
-    date.setFullYear(-213);
-    assertEquals('213 BC', fmt.format(date));
+      date.setFullYear(-213);
+      assertEquals('213 BC', fmt.format(date));
 
-    goog.i18n.DateTimePatterns = DateTimePatterns_de;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_de;
-    fmt = new DateTimeFormat(goog.i18n.DateTimePatterns.YEAR_FULL_WITH_ERA);
+      replacer.replace(goog, 'LOCALE', 'de');
+      replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_de);
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_de);
+      fmt = new DateTimeFormat(DateTimePatterns_de.YEAR_FULL_WITH_ERA);
 
-    date.setFullYear(2013);
-    assertEquals('2013 n. Chr.', fmt.format(date));
+      date.setFullYear(2013);
+      assertEquals('2013 n. Chr.', fmt.format(date));
 
-    date.setFullYear(213);
-    assertEquals('213 n. Chr.', fmt.format(date));
+      date.setFullYear(213);
+      assertEquals('213 n. Chr.', fmt.format(date));
 
-    date.setFullYear(11);
-    assertEquals('11 n. Chr.', fmt.format(date));
+      date.setFullYear(11);
+      assertEquals('11 n. Chr.', fmt.format(date));
 
-    date.setFullYear(-213);
-    assertEquals('213 v. Chr.', fmt.format(date));
+      date.setFullYear(-213);
+      assertEquals('213 v. Chr.', fmt.format(date));
 
-    goog.i18n.DateTimePatterns = DateTimePatterns_ja;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_ja;
-    fmt = new DateTimeFormat(goog.i18n.DateTimePatterns.YEAR_FULL_WITH_ERA);
+      replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_ja);
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_ja);
+      fmt = new DateTimeFormat(DateTimePatterns_ja.YEAR_FULL_WITH_ERA);
 
-    date.setFullYear(2013);
-    assertEquals('西暦2013年', fmt.format(date));
+      date.setFullYear(2013);
+      assertEquals('西暦2013年', fmt.format(date));
 
-    date.setFullYear(213);
-    assertEquals('西暦213年', fmt.format(date));
+      date.setFullYear(213);
+      assertEquals('西暦213年', fmt.format(date));
 
-    date.setFullYear(11);
-    assertEquals('西暦11年', fmt.format(date));
+      date.setFullYear(11);
+      assertEquals('西暦11年', fmt.format(date));
 
-    date.setFullYear(-213);
-    assertEquals('紀元前213年', fmt.format(date));
+      date.setFullYear(-213);
+      assertEquals('紀元前213年', fmt.format(date));
+    }
   },
 
   // Expected results from ICU4J v51. One entry will change in v52.
   // These cover all combinations of FIRSTDAYOFWEEK / FIRSTWEEKCUTOFFDAY in use.
   testWeekInYearI18n() {
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_bn_BD;
-    assertEquals('bn_BD', '১১১১১২২', weekInYearFor7Days());
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_en_IE;
-    assertEquals('en_IE', '1111112', weekInYearFor7Days());
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_fr_DJ;
-    assertEquals('fr_DJ', '1111222', weekInYearFor7Days());
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_he_IL;
-    assertEquals('he_IL', '1111122', weekInYearFor7Days());
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_ar_SA;
-    assertEquals('ar_SA', '١١١١١٢٢', weekInYearFor7Days());
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_ar_AE;
-    assertEquals('ar_AE', '١١١١٢٢٢', weekInYearFor7Days());
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_en_IN;
-    assertEquals('en_IN', '1111122', weekInYearFor7Days());
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_en_GB;
-    assertEquals('en_GB', '1111112', weekInYearFor7Days());
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_en_US;
-    assertEquals('en_US', '1111122', weekInYearFor7Days());
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_ro_RO;
-    assertEquals('ro_RO', '1111112', weekInYearFor7Days());
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_bn_BD);
+      assertEquals('bn_BD', '১১১১১২২', weekInYearFor7Days());
+
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_en_IE);
+      assertEquals('en_IE', '1111112', weekInYearFor7Days());
+
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_fr_DJ);
+      assertEquals('fr_DJ', '1111222', weekInYearFor7Days());
+
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_he_IL);
+      assertEquals('he_IL', '1111122', weekInYearFor7Days());
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_ar_SA);
+      assertEquals('ar_SA', '١١١١١٢٢', weekInYearFor7Days());
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_ar_AE);
+      assertEquals('ar_AE', '١١١١٢٢٢', weekInYearFor7Days());
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_en_IN);
+      assertEquals('en_IN', '1111122', weekInYearFor7Days());
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_en_GB);
+      assertEquals('en_GB', '1111112', weekInYearFor7Days());
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_en_US);
+      assertEquals('en_US', '1111122', weekInYearFor7Days());
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_ro_RO);
+      assertEquals('ro_RO', '1111112', weekInYearFor7Days());
+    }
   },
 
   // Regression for b/11567443 (no method 'getHours' when formatting a
   // goog.date.Date)
   test_variousDateTypes() {
-    goog.i18n.DateTimePatterns = DateTimePatterns_fr;
-    goog.i18n.DateTimeSymbols = DateTimeSymbols_fr;
-
-    const fmt = new DateTimeFormat(DateTimeFormat.Format.MEDIUM_DATETIME);
-
-    const date = new Date(2006, 6, 27, 13, 10, 42, 250);
-    assertEquals('27 juil. 2006, 13:10:42', fmt.format(date));
-
-    const gdatetime = new DateTime(2006, 6, 27, 13, 10, 42, 250);
-    assertEquals('27 juil. 2006, 13:10:42', fmt.format(gdatetime));
-
-    const gdate = new DateDate(2006, 6, 27);
-    const fmtDate = new DateTimeFormat(DateTimeFormat.Format.MEDIUM_DATE);
-    assertEquals('27 juil. 2006', fmtDate.format(gdatetime));
-    try {
-      fmt.format(gdate);
-      fail('Should have thrown exception.');
-    } catch (e) {
+    replacer.replace(goog, 'LOCALE', 'fr');
+    replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_fr);
+    replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_fr);
+
+
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+
+      const fmt = new DateTimeFormat(DateTimeFormat.Format.MEDIUM_DATETIME);
+
+      const date = new Date(2006, 6, 27, 13, 10, 42, 250);
+      let expected = '27 juil. 2006, 13:10:42';
+      let alternate = '27 juil. 2006 à 13:10:42';
+      let result = removeLtrMarkers(fmt.format(date));
+
+      // Some browsers use the alternate form.
+      if (nativeMode) {
+        assertTrue(
+            'Native 27 juil = ' + result,
+            expected === result || alternate === result);
+      } else {
+        // Polyfill mode
+        assertEquals(expected, result);
+      }
+
+      const gdatetime = new DateTime(2006, 6, 27, 13, 10, 42, 250);
+      expected = '27 juil. 2006, 13:10:42';
+      alternate = '27 juil. 2006 à 13:10:42';
+      result = removeLtrMarkers(fmt.format(gdatetime));
+
+      if (nativeMode) {
+        assertTrue(
+            'gdatetime MEDIUM_DATETIME juil. result = ' + result,
+            expected === result || alternate === result);
+      } else {
+        assertEquals(expected, result);
+      }
+
+      const gdate = new DateDate(2006, 6, 27);
+      const fmtDate = new DateTimeFormat(DateTimeFormat.Format.MEDIUM_DATE);
+
+      expected = '27 juil. 2006';
+      alternate = removeDirectionMarkers('27/07/2006');
+      result = removeDirectionMarkers(fmtDate.format(gdatetime));
+
+      assertTrue(
+          'Native mode = ' + nativeMode + ' gdate MEDIUM_DATE = ' + result,
+          result === expected || result === alternate);
+
+      if (!nativeMode) {
+        try {
+          fmt.format(gdate);
+          fail('Should have thrown exception.');
+        } catch (e) {
+        }
+      } else {
+        // Native mode returns midnight without explicit time set.
+        // Make better match to remove commas.
+        const result = removeDirectionMarkers(fmt.format(gdate))
+                           .replace(/[\u002c\u060c]/g, '');
+        expected = '27 juil. 2006 0:00:00';
+        const alternate = '27 juil. 2006 à 00:00:00';
+        const alternate2 = '27 juil. 2006 à 0:00:00';
+        const alternate3 = '27 juil. 2006 00:00:00';
+        assertTrue(
+            'Midnight result = ' + result,
+            result === expected || result === alternate ||
+                result === alternate2 || result === alternate3);
+      }
     }
   },
 
@@ -972,4 +1439,275 @@ testSuite({
     } catch (e) {
     }
   },
+
+  testNativeModeEnglishStdPatterns() {
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(goog, 'LOCALE', 'en-US');
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+
+      const fmt = new DateTimeFormat(DateTimeFormat.Format.MEDIUM_DATETIME);
+
+      assertEquals(10, DateTimeFormat.Format.MEDIUM_DATETIME);
+
+      const date = new Date(2006, 6, 27, 13, 10, 42, 250);
+      let result = fmt.format(date);
+      let expected = 'Jul 27, 2006, 1:10:42 PM';
+      result = removeLtrMarkers(result);
+      let matched =
+          /Jul 27, 2006(,| at)? 1:10:42 PM/.test(result);  // Optional comma
+      assertTrue('Expected match = ' + result, matched);
+
+      const gdatetime = new DateTime(2006, 6, 27, 13, 10, 42, 250);
+
+      result = removeLtrMarkers(fmt.format(gdatetime));
+      matched = /Jul 27, 2006(,| at)? 1:10:42 PM/.test(result);  // Optional comma
+      if (matched) {
+        assertTrue(matched);
+      } else {
+        assertEquals('Jul 27, 2006, 1:10:42 PM', result);
+      }
+
+      const fmtDate = new DateTimeFormat(DateTimeFormat.Format.MEDIUM_DATE);
+      result = removeDirectionMarkers(fmtDate.format(gdatetime));
+      expected = 'Jul 27, 2006';
+      assertEquals(expected, result);
+
+      const fmt0 = new DateTimeFormat(DateTimeFormat.Format.FULL_DATE);
+      result = removeDirectionMarkers(fmt0.format(gdatetime));
+      assertEquals('Thursday, July 27, 2006', result);
+
+      const fmt1 = new DateTimeFormat(DateTimeFormat.Format.SHORT_TIME);
+      result = removeDirectionMarkers(fmt1.format(gdatetime));
+      assertEquals('1:10 PM', result);
+
+      const fmt2 = new DateTimeFormat(DateTimeFormat.Format.FULL_DATETIME);
+      result = removeDirectionMarkers(fmt2.format(gdatetime));
+
+      if (nativeMode) {
+        expected = 'Thursday, July 27, 2006 at 1:10:42 PM Pacific Daylight Time';
+      } else {
+        expected = 'Thursday, July 27, 2006 at 1:10:42 PM UTC-7';
+      }
+      assertEquals('nativeMode=' + nativeMode, expected, result);
+
+      const fmt3 = new DateTimeFormat(DateTimeFormat.Format.LONG_DATE);
+      result = removeDirectionMarkers(fmt3.format(gdatetime));
+      assertEquals('July 27, 2006', result);
+    }
+  },
+
+  test_FrenchPatternStrings() {
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+
+      replacer.replace(goog.i18n, 'DateTimePatterns', DateTimePatterns_fr);
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_fr);
+      replacer.replace(goog, 'LOCALE', 'fr');
+
+      const fmt = new DateTimeFormat(DateTimePatterns_fr.YEAR_FULL);
+
+      const date = new Date(2006, 6, 27, 13, 10, 42, 250);
+      let result = fmt.format(date);
+      assertEquals('2006', result);
+
+      const fmt1 = new DateTimeFormat(DateTimePatterns_fr.YEAR_FULL_WITH_ERA);
+      result = fmt1.format(date);
+      assertEquals('2006 ap. J.-C.', result);
+
+      const fmt2 = new DateTimeFormat(DateTimePatterns_fr.MONTH_DAY_SHORT);
+      result = fmt2.format(date);
+      assertEquals('27/07', result);
+
+      const fmt3 =
+          new DateTimeFormat(DateTimePatterns_fr.MONTH_DAY_TIME_ZONE_SHORT);
+      result = fmt3.format(date);
+      assertEquals('27 juil., 13:10 UTC-7', result);
+    }
+  },
+
+  test_NativeModeWithUnsupportedLocale() {
+    setNativeMode(true);
+    if (goog.labs.userAgent.browser.isIE() ||
+        goog.global.Intl == undefined ||
+        goog.global.Intl.DateTimeFormat == undefined) {
+      return;
+    }
+
+    // Sumerian will default to English.
+    replacer.replace(goog, 'LOCALE', 'sux');
+
+    const nativeSetting = getNativeMode();
+    assert(nativeSetting);
+
+    const fmt = new DateTimeFormat(DateTimeFormat.Format.MEDIUM_DATETIME);
+
+    const date = new Date(2006, 6, 27, 13, 10, 42, 250);
+    let result = removeLtrMarkers(fmt.format(date)).replace(/2006,/g, '2006');
+    let matched = /Jul 27, 2006 (at )?1:10:42 PM/.test(result);
+    assertTrue('MEDIUM_DATETIME result = ' + result,
+               matched);
+
+    const fmt1 = new DateTimeFormat(DateTimePatterns.YEAR_FULL);
+
+    result = fmt1.format(date);
+    assertEquals('2006', result);
+  },
+
+  testNonAsciiDigitsNative() {
+    const date = new Date(2006, 6, 27, 13, 10, 42, 250);
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+
+      // Arabic with ASCII
+      replacer.replace(goog, 'LOCALE', 'ar');
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_ar);
+      const ar = new DateTimeFormat(DateTimeFormat.Format.SHORT_DATE);
+      let expected = removeDirectionMarkers('27‏/7‏/2006');
+      let result = removeDirectionMarkers(ar.format(date));
+      assertEquals('ar', expected, result);
+
+      // Egyptian Arabic
+      replacer.replace(goog, 'LOCALE', 'ar-EG');
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_ar_EG);
+      const ar_EG = new DateTimeFormat(DateTimeFormat.Format.SHORT_DATE);
+      expected = '٢٧‏/٧‏/٢٠٠٦';
+      let expected2 = '٢٧‏/٠٧‏/٢٠٠٦';  // Zero digit in month
+      result = ar_EG.format(date);
+      result = removeDirectionMarkers(result);
+      assertTrue(
+          'ar-EG',
+          removeDirectionMarkers(expected) == removeDirectionMarkers(result) ||
+              removeDirectionMarkers(expected2) ==
+                  removeDirectionMarkers(result));
+
+      // Bengali
+      replacer.replace(goog, 'LOCALE', 'bn');
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_bn);
+      const bn = new DateTimeFormat(DateTimeFormat.Format.SHORT_DATE);
+      expected = '২৭/৭/০৬';
+      result = bn.format(date);
+      assertEquals('bn', expected, result);
+
+      replacer.replace(goog, 'LOCALE', 'bn_BD');
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_bn);
+      const bn_BD = new DateTimeFormat(DateTimeFormat.Format.SHORT_DATE);
+      result = bn_BD.format(date);
+      assertEquals('bn_BD', expected, result);
+
+      // Persian / Farsi
+      replacer.replace(goog, 'LOCALE', 'fa');
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_fa);
+      const fa = new DateTimeFormat(DateTimeFormat.Format.SHORT_DATE);
+      expected =
+          removeDirectionMarkers('۲۰۰۶/۷/۲۷');  // Different from Arabic digits
+      result = removeDirectionMarkers(fa.format(date));
+      assertEquals('Farsi digits result = ' + result, expected, result);
+
+      // Malayalam
+      replacer.replace(goog, 'LOCALE', 'ml');
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_ml);
+      const ml = new DateTimeFormat(DateTimeFormat.Format.SHORT_DATE);
+      expected = '27/7/06';
+      result = ml.format(date);
+      assertEquals('Malayalam digits result = ' + result, expected, result);
+
+      // Marathi
+      replacer.replace(goog, 'LOCALE', 'mr');
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_mr);
+      const mr = new DateTimeFormat(DateTimeFormat.Format.SHORT_DATE);
+      expected = '२७/७/०६';
+      result = mr.format(date);
+      assertEquals('Marathi digits result = ' + result, expected, result);
+
+      // Myanmar
+      replacer.replace(goog, 'LOCALE', 'my');
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_my);
+      const my = new DateTimeFormat(DateTimeFormat.Format.SHORT_DATE);
+      result = my.format(date);
+      expected = '၂၇-၀၇-၀၆';
+      let alternate = '၇/၂၇/၀၆';  // Chrome native gregorian
+      assertTrue(
+          'Myanmar digits = ' + result,
+          expected === result || alternate === result);
+
+      // Nepali
+      replacer.replace(goog, 'LOCALE', 'ne');
+      replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_ne);
+      const ne = new DateTimeFormat(DateTimeFormat.Format.SHORT_DATE);
+      result = ne.format(date);
+      expected = '०६/७/२७';
+      alternate = '७/२७/०६';  // Chrome native gregorian
+      assertTrue(
+          'Nepali digits = ' + result,
+          expected === result || alternate == result);
+    }
+  },
+
+  /** @suppress {checkTypes} suppression added to enable type checking */
+  testWebMapsDirectionsCase() {
+    // Verify that UTC and locale times are formatted for the correct timezone.
+
+    replacer.replace(goog, 'LOCALE', 'en');
+
+    const utcTime = UtcDateTime.fromIsoString('2010-01-01');
+    const localeTime = new Date('2010-01-01');
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+
+      let fmt = new DateTimeFormat(DateTimeFormat.Format.SHORT_TIME);
+      let result = fmt.format(utcTime);
+      assertEquals('12:00 AM', result);
+
+      // Formatter needs to have its timzone changed.
+      // Change to non-UTC time
+      result = fmt.format(localeTime);
+      assertEquals('4:00 PM', result);
+
+      // Change back to UTC time
+      result = fmt.format(utcTime);
+      assertEquals('12:00 AM', result);
+
+      // Another change to non-UTC time
+      result = fmt.format(localeTime);
+      assertEquals('4:00 PM', result);
+    }
+  },
+
+  /** @suppress {checkTypes} suppression added to enable type checking */
+  testShortDate() {
+    const date = new Date(2012, 4, 8);
+    replacer.replace(goog.i18n, 'DateTimeSymbols', DateTimeSymbols_en);
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+
+      const fmt = new DateTimeFormat(DateTimeFormat.Format.SHORT_DATE,
+                                   DateTimeSymbols);
+       let result = fmt.format(date);
+      assertEquals('5/8/12', result);
+
+      const fmt2 = new DateTimeFormat(DateTimeFormat.Format.SHORT_DATETIME,
+                                   DateTimeSymbols);
+      result = fmt2.format(date);
+      assertEquals('5/8/12, 12:00 AM', result);
+    }
+  },
+
+  testNoLocaleSet() {
+    const date = new Date(2012, 4, 8);
+    replacer.replace(goog, 'LOCALE', '');
+    for (let nativeMode of testECMAScriptOptions) {
+      replacer.replace(
+          LocaleFeature, 'USE_ECMASCRIPT_I18N_DATETIMEF', nativeMode);
+      const fmt = new DateTimeFormat(DateTimeFormat.Format.SHORT_DATE);
+      assertTrue(fmt !== null);
+      const result = fmt.format(date);
+      assertEquals('5/8/12', result);
+    }
+  },
+
 });
diff --git a/closure/goog/i18n/localefeature.js b/closure/goog/i18n/localefeature.js
index 6ed09ed740..ea0ddd432c 100644
--- a/closure/goog/i18n/localefeature.js
+++ b/closure/goog/i18n/localefeature.js
@@ -101,3 +101,12 @@ exports.USE_ECMASCRIPT_I18N_NUMFORMAT =
 exports.USE_ECMASCRIPT_I18N_PLURALRULES =
     (!exports.ECMASCRIPT_INTL_OPT_OUT && goog.FEATURESET_YEAR >= 2021 &&
      exports.ECMASCRIPT_COMMON_LOCALES_2019);
+
+/**
+ * @define {boolean} USE_ECMASCRIPT_I18N_DATETIMEF is evaluted to enable
+ * ECMAScript support for Intl.DateTimeFormat support in
+ * browsers based on the locale. Browsers that are considered include:
+ * Chrome, Firefox, Edge, and Safari.
+ */
+exports.USE_ECMASCRIPT_I18N_DATETIMEF =
+    (exports.USE_ECMASCRIPT_I18N && !exports.ECMASCRIPT_INTL_OPT_OUT);
diff --git a/closure/goog/i18n/nativelocaledigits.js b/closure/goog/i18n/nativelocaledigits.js
new file mode 100644
index 0000000000..6364dabbc4
--- /dev/null
+++ b/closure/goog/i18n/nativelocaledigits.js
@@ -0,0 +1,40 @@
+/**
+ * @license
+ * Copyright The Closure Library Authors.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+// clang-format off
+
+goog.module('goog.i18n.NativeLocaleDigits');
+
+/**
+ * @fileoverview Provides map of locales to script identifiers
+ * where locales require specific digits other than ASCII.
+ */
+
+/**
+ * Type of map from locale string to script codes
+ * @typedef {!Object<string,string>}
+ */
+let LocaleScriptMap;
+
+/** @typedef {{LocaleScriptMap}} */
+exports.LocaleScriptMap;
+
+/**
+ * Native digit codes in ECMAScript Intl objects for locales
+ * where native digits are prescribed and Intl data is generally available.
+ * This is designed for classes that create locale-specific
+ * numbers. Examples include number and date/time formatting.
+ * @const {!LocaleScriptMap}
+ */
+exports.FormatWithLocaleDigits = {
+  'ar': 'latn',
+  'ar-EG': 'arab',
+  'bn': 'beng',
+  'fa': 'arabext',
+  'mr': 'deva',
+  'my': 'mymr',
+  'ne': 'deva'
+};
diff --git a/closure/goog/i18n/numberformat.js b/closure/goog/i18n/numberformat.js
index f1ba73f133..6746ae4ad3 100644
--- a/closure/goog/i18n/numberformat.js
+++ b/closure/goog/i18n/numberformat.js
@@ -18,6 +18,9 @@ goog.provide('goog.i18n.NumberFormat.Format');
 goog.require('goog.asserts');
 goog.require('goog.i18n.CompactNumberFormatSymbols');
 
+goog.require('goog.i18n.LocaleFeature');
+goog.require('goog.i18n.NativeLocaleDigits');
+
 goog.require('goog.i18n.NumberFormatSymbols');
 goog.require('goog.i18n.NumberFormatSymbolsType');
 goog.require('goog.i18n.NumberFormatSymbols_u_nu_latn');
@@ -26,6 +29,12 @@ goog.require('goog.i18n.currency.CurrencyInfo');
 goog.require('goog.math');
 goog.require('goog.string');
 
+goog.scope(function() {
+
+// For referencing modules
+const LocaleFeature = goog.module.get('goog.i18n.LocaleFeature');
+const NativeLocaleDigits = goog.module.get('goog.i18n.NativeLocaleDigits');
+
 /**
  * Constructor of NumberFormat.
  * @param {number|string} pattern The number that indicates a predefined
@@ -116,6 +125,7 @@ goog.i18n.NumberFormat = function(
    * goog.i18n.NumberFormat('#,##,###') should have [3,2] where 2 is the
    * repeated number group following a fixed number grouping of size 3.
    * @private {!Array<number>}
+   * @const
    */
   this.groupingArray_ = [];
 
@@ -135,7 +145,7 @@ goog.i18n.NumberFormat = function(
   this.baseFormattingNumber_ = null;
 
   // Original numeric pattern. Needed because JS modifies this.pattern_*/
-  /** @private {number} */
+  /** @const @private {number} */
   this.inputPattern_ = (typeof pattern === 'number') ? pattern : -1;
 
   /** @private {string} */
@@ -202,22 +212,6 @@ goog.i18n.NumberFormat.CompactStyle = {
  */
 goog.i18n.NumberFormat.enforceAsciiDigits_ = false;
 
-
-/**
- * Native digit codes in EMACScript Intl objects for locales
- * where native digits are prescribed and Intl data is
- * generally available.
- * @private
- */
-goog.i18n.NumberFormat.NativeLocaleDigits_ = {
-  'ar': 'latn',
-  'ar-EG': 'arab',
-  'bn': 'beng',
-  'fa': 'arabext',
-  'mr': 'deva',
-  'my': 'mymr',
-  'ne': 'deva'
-};
 /**
  * Set if the usage of Ascii digits in formatting should be enforced.
  * NOTE: This function must be called before constructing NumberFormat.
@@ -790,11 +784,11 @@ goog.i18n.NumberFormat.prototype.SetUpIntlFormatter_ = function(inputPattern) {
     if (goog.LOCALE) {
       locale = goog.LOCALE.replace('_', '-');
     }
-    if (!goog.i18n.NumberFormat.enforceAsciiDigits_ &&
-        locale in goog.i18n.NumberFormat.NativeLocaleDigits_) {
+    if (locale && !goog.i18n.NumberFormat.enforceAsciiDigits_ &&
+        (locale in NativeLocaleDigits.FormatWithLocaleDigits)) {
       // Sets native digits for same locales as polyfill.
       options.numberingSystem =
-          goog.i18n.NumberFormat.NativeLocaleDigits_[locale];
+          NativeLocaleDigits.FormatWithLocaleDigits[locale];
     }
     // This works with undefined locale or empty string.
     this.intlFormatter_ = new Intl.NumberFormat(locale, options);
@@ -1467,6 +1461,7 @@ goog.i18n.NumberFormat.prototype.getDigit_ = function(ch) {
  * A zero digit character.
  * @type {string}
  * @private
+ * @const
  */
 goog.i18n.NumberFormat.PATTERN_ZERO_DIGIT_ = '0';
 
@@ -1475,6 +1470,7 @@ goog.i18n.NumberFormat.PATTERN_ZERO_DIGIT_ = '0';
  * A grouping separator character.
  * @type {string}
  * @private
+ * @const
  */
 goog.i18n.NumberFormat.PATTERN_GROUPING_SEPARATOR_ = ',';
 
@@ -1483,6 +1479,7 @@ goog.i18n.NumberFormat.PATTERN_GROUPING_SEPARATOR_ = ',';
  * A decimal separator character.
  * @type {string}
  * @private
+ * @const
  */
 goog.i18n.NumberFormat.PATTERN_DECIMAL_SEPARATOR_ = '.';
 
@@ -1491,6 +1488,7 @@ goog.i18n.NumberFormat.PATTERN_DECIMAL_SEPARATOR_ = '.';
  * A per mille character.
  * @type {string}
  * @private
+ * @const
  */
 goog.i18n.NumberFormat.PATTERN_PER_MILLE_ = '\u2030';
 
@@ -1499,6 +1497,7 @@ goog.i18n.NumberFormat.PATTERN_PER_MILLE_ = '\u2030';
  * A percent character.
  * @type {string}
  * @private
+ * @const
  */
 goog.i18n.NumberFormat.PATTERN_PERCENT_ = '%';
 
@@ -1507,6 +1506,7 @@ goog.i18n.NumberFormat.PATTERN_PERCENT_ = '%';
  * A digit character.
  * @type {string}
  * @private
+ * @const
  */
 goog.i18n.NumberFormat.PATTERN_DIGIT_ = '#';
 
@@ -1515,6 +1515,7 @@ goog.i18n.NumberFormat.PATTERN_DIGIT_ = '#';
  * A separator character.
  * @type {string}
  * @private
+ * @const
  */
 goog.i18n.NumberFormat.PATTERN_SEPARATOR_ = ';';
 
@@ -1523,6 +1524,7 @@ goog.i18n.NumberFormat.PATTERN_SEPARATOR_ = ';';
  * An exponent character.
  * @type {string}
  * @private
+ * @const
  */
 goog.i18n.NumberFormat.PATTERN_EXPONENT_ = 'E';
 
@@ -1531,6 +1533,7 @@ goog.i18n.NumberFormat.PATTERN_EXPONENT_ = 'E';
  * A plus character.
  * @type {string}
  * @private
+ * @const
  */
 goog.i18n.NumberFormat.PATTERN_PLUS_ = '+';
 
@@ -1539,6 +1542,7 @@ goog.i18n.NumberFormat.PATTERN_PLUS_ = '+';
  * A generic currency sign character.
  * @type {string}
  * @private
+ * @const
  */
 goog.i18n.NumberFormat.PATTERN_CURRENCY_SIGN_ = '\u00A4';
 
@@ -1547,6 +1551,7 @@ goog.i18n.NumberFormat.PATTERN_CURRENCY_SIGN_ = '\u00A4';
  * A quote character.
  * @type {string}
  * @private
+ * @const
  */
 goog.i18n.NumberFormat.QUOTE_ = '\'';
 
@@ -1833,6 +1838,7 @@ goog.i18n.NumberFormat.FormattedPart;
 /**
  * The empty unit, corresponding to a base of 0.
  * @private {!goog.i18n.NumberFormat.CompactNumberUnit}
+ * @const
  */
 goog.i18n.NumberFormat.NULL_UNIT_ = {
   divisorBase: 0,
@@ -2138,3 +2144,4 @@ goog.i18n.NumberFormat.prototype.isCurrencyCodeBeforeValue = function() {
   // If not, we have bigger problems than this.
   return posCurrSymbol < posCurrValue;
 };
+});  // End of scope for module data