From 8fa200aff08e4c79e3fa31169d1b757c6be254f0 Mon Sep 17 00:00:00 2001
From: Brendan Kenny <bckenny@gmail.com>
Date: Wed, 1 May 2024 00:36:15 -0500
Subject: [PATCH 01/14] use union of metric types more broadly

---
 src/attribution/onCLS.ts  | 21 ++++++---------------
 src/attribution/onFCP.ts  | 21 ++++++---------------
 src/attribution/onFID.ts  | 21 ++++++---------------
 src/attribution/onINP.ts  | 37 ++++++++++++++-----------------------
 src/attribution/onLCP.ts  | 15 +++++----------
 src/attribution/onTTFB.ts | 21 ++++++---------------
 src/onCLS.ts              | 12 +++++-------
 src/onFCP.ts              | 14 ++++++--------
 src/onFID.ts              |  8 +++++---
 src/onINP.ts              | 14 ++++++--------
 src/onLCP.ts              | 14 ++++++--------
 src/onTTFB.ts             | 11 +++++------
 src/types/base.ts         | 39 ++++++++++++++++-----------------------
 src/types/cls.ts          | 18 ++----------------
 src/types/fcp.ts          | 18 ++----------------
 src/types/fid.ts          | 18 ++----------------
 src/types/inp.ts          | 18 ++----------------
 src/types/lcp.ts          | 18 ++----------------
 src/types/ttfb.ts         | 18 ++----------------
 19 files changed, 104 insertions(+), 252 deletions(-)

diff --git a/src/attribution/onCLS.ts b/src/attribution/onCLS.ts
index 453e25b6..5fca98cb 100644
--- a/src/attribution/onCLS.ts
+++ b/src/attribution/onCLS.ts
@@ -17,13 +17,7 @@
 import {getLoadState} from '../lib/getLoadState.js';
 import {getSelector} from '../lib/getSelector.js';
 import {onCLS as unattributedOnCLS} from '../onCLS.js';
-import {
-  CLSReportCallback,
-  CLSReportCallbackWithAttribution,
-  CLSMetric,
-  CLSMetricWithAttribution,
-  ReportOpts,
-} from '../types.js';
+import {CLSMetric, CLSMetricWithAttribution, ReportOpts} from '../types.js';
 
 const getLargestLayoutShiftEntry = (entries: LayoutShift[]) => {
   return entries.reduce((a, b) => (a && a.value > b.value ? a : b));
@@ -77,14 +71,11 @@ const attributeCLS = (metric: CLSMetric): void => {
  * during the same page load._
  */
 export const onCLS = (
-  onReport: CLSReportCallbackWithAttribution,
+  onReport: (metric: CLSMetricWithAttribution) => void,
   opts?: ReportOpts,
 ) => {
-  unattributedOnCLS(
-    ((metric: CLSMetricWithAttribution) => {
-      attributeCLS(metric);
-      onReport(metric);
-    }) as CLSReportCallback,
-    opts,
-  );
+  unattributedOnCLS((metric: CLSMetric) => {
+    attributeCLS(metric);
+    onReport(metric as CLSMetricWithAttribution);
+  }, opts);
 };
diff --git a/src/attribution/onFCP.ts b/src/attribution/onFCP.ts
index 54f23110..649f96ed 100644
--- a/src/attribution/onFCP.ts
+++ b/src/attribution/onFCP.ts
@@ -19,13 +19,7 @@ import {getLoadState} from '../lib/getLoadState.js';
 import {getNavigationEntry} from '../lib/getNavigationEntry.js';
 import {isInvalidTimestamp} from '../lib/isInvalidTimestamp.js';
 import {onFCP as unattributedOnFCP} from '../onFCP.js';
-import {
-  FCPMetric,
-  FCPMetricWithAttribution,
-  FCPReportCallback,
-  FCPReportCallbackWithAttribution,
-  ReportOpts,
-} from '../types.js';
+import {FCPMetric, FCPMetricWithAttribution, ReportOpts} from '../types.js';
 
 const attributeFCP = (metric: FCPMetric): void => {
   if (metric.entries.length) {
@@ -64,14 +58,11 @@ const attributeFCP = (metric: FCPMetric): void => {
  * value is a `DOMHighResTimeStamp`.
  */
 export const onFCP = (
-  onReport: FCPReportCallbackWithAttribution,
+  onReport: (metric: FCPMetricWithAttribution) => void,
   opts?: ReportOpts,
 ) => {
-  unattributedOnFCP(
-    ((metric: FCPMetricWithAttribution) => {
-      attributeFCP(metric);
-      onReport(metric);
-    }) as FCPReportCallback,
-    opts,
-  );
+  unattributedOnFCP((metric: FCPMetric) => {
+    attributeFCP(metric);
+    onReport(metric as FCPMetricWithAttribution);
+  }, opts);
 };
diff --git a/src/attribution/onFID.ts b/src/attribution/onFID.ts
index 138c92e6..a75a2577 100644
--- a/src/attribution/onFID.ts
+++ b/src/attribution/onFID.ts
@@ -17,13 +17,7 @@
 import {getLoadState} from '../lib/getLoadState.js';
 import {getSelector} from '../lib/getSelector.js';
 import {onFID as unattributedOnFID} from '../onFID.js';
-import {
-  FIDMetric,
-  FIDMetricWithAttribution,
-  FIDReportCallback,
-  FIDReportCallbackWithAttribution,
-  ReportOpts,
-} from '../types.js';
+import {FIDMetric, FIDMetricWithAttribution, ReportOpts} from '../types.js';
 
 const attributeFID = (metric: FIDMetric): void => {
   const fidEntry = metric.entries[0];
@@ -46,14 +40,11 @@ const attributeFID = (metric: FIDMetric): void => {
  * page, it's possible that it will not be reported for some page loads._
  */
 export const onFID = (
-  onReport: FIDReportCallbackWithAttribution,
+  onReport: (metric: FIDMetricWithAttribution) => void,
   opts?: ReportOpts,
 ) => {
-  unattributedOnFID(
-    ((metric: FIDMetricWithAttribution) => {
-      attributeFID(metric);
-      onReport(metric);
-    }) as FIDReportCallback,
-    opts,
-  );
+  unattributedOnFID((metric: FIDMetric) => {
+    attributeFID(metric);
+    onReport(metric as FIDMetricWithAttribution);
+  }, opts);
 };
diff --git a/src/attribution/onINP.ts b/src/attribution/onINP.ts
index 3b6920c2..378ad2c2 100644
--- a/src/attribution/onINP.ts
+++ b/src/attribution/onINP.ts
@@ -23,13 +23,7 @@ import {
 import {observe} from '../lib/observe.js';
 import {whenIdle} from '../lib/whenIdle.js';
 import {onINP as unattributedOnINP} from '../onINP.js';
-import {
-  INPMetric,
-  INPMetricWithAttribution,
-  INPReportCallback,
-  INPReportCallbackWithAttribution,
-  ReportOpts,
-} from '../types.js';
+import {INPMetric, INPMetricWithAttribution, ReportOpts} from '../types.js';
 
 interface pendingEntriesGroup {
   startTime: DOMHighResTimeStamp;
@@ -270,25 +264,22 @@ const attributeINP = (metric: INPMetric): void => {
  * during the same page load._
  */
 export const onINP = (
-  onReport: INPReportCallbackWithAttribution,
+  onReport: (metric: INPMetricWithAttribution) => void,
   opts?: ReportOpts,
 ) => {
   if (!loafObserver) {
     loafObserver = observe('long-animation-frame', handleLoAFEntries);
   }
-  unattributedOnINP(
-    ((metric: INPMetricWithAttribution) => {
-      // Queue attribution and reporting in the next idle task.
-      // This is needed to increase the chances that all event entries that
-      // occurred between the user interaction and the next paint
-      // have been dispatched. Note: there is currently an experiment
-      // running in Chrome (EventTimingKeypressAndCompositionInteractionId)
-      // 123+ that if rolled out fully would make this no longer necessary.
-      whenIdle(() => {
-        attributeINP(metric);
-        onReport(metric);
-      });
-    }) as INPReportCallback,
-    opts,
-  );
+  unattributedOnINP((metric: INPMetric) => {
+    // Queue attribution and reporting in the next idle task.
+    // This is needed to increase the chances that all event entries that
+    // occurred between the user interaction and the next paint
+    // have been dispatched. Note: there is currently an experiment
+    // running in Chrome (EventTimingKeypressAndCompositionInteractionId)
+    // 123+ that if rolled out fully would make this no longer necessary.
+    whenIdle(() => {
+      attributeINP(metric);
+      onReport(metric as INPMetricWithAttribution);
+    });
+  }, opts);
 };
diff --git a/src/attribution/onLCP.ts b/src/attribution/onLCP.ts
index 5b174368..aeba48fb 100644
--- a/src/attribution/onLCP.ts
+++ b/src/attribution/onLCP.ts
@@ -22,8 +22,6 @@ import {
   LCPAttribution,
   LCPMetric,
   LCPMetricWithAttribution,
-  LCPReportCallback,
-  LCPReportCallbackWithAttribution,
   ReportOpts,
 } from '../types.js';
 
@@ -105,14 +103,11 @@ const attributeLCP = (metric: LCPMetric) => {
  * been determined.
  */
 export const onLCP = (
-  onReport: LCPReportCallbackWithAttribution,
+  onReport: (metric: LCPMetricWithAttribution) => void,
   opts?: ReportOpts,
 ) => {
-  unattributedOnLCP(
-    ((metric: LCPMetricWithAttribution) => {
-      attributeLCP(metric);
-      onReport(metric);
-    }) as LCPReportCallback,
-    opts,
-  );
+  unattributedOnLCP((metric: LCPMetric) => {
+    attributeLCP(metric);
+    onReport(metric as LCPMetricWithAttribution);
+  }, opts);
 };
diff --git a/src/attribution/onTTFB.ts b/src/attribution/onTTFB.ts
index 7c1876e4..3f267c04 100644
--- a/src/attribution/onTTFB.ts
+++ b/src/attribution/onTTFB.ts
@@ -15,13 +15,7 @@
  */
 
 import {onTTFB as unattributedOnTTFB} from '../onTTFB.js';
-import {
-  TTFBMetric,
-  TTFBMetricWithAttribution,
-  TTFBReportCallback,
-  TTFBReportCallbackWithAttribution,
-  ReportOpts,
-} from '../types.js';
+import {TTFBMetric, TTFBMetricWithAttribution, ReportOpts} from '../types.js';
 
 const attributeTTFB = (metric: TTFBMetric): void => {
   if (metric.entries.length) {
@@ -91,14 +85,11 @@ const attributeTTFB = (metric: TTFBMetric): void => {
  * and server processing time.
  */
 export const onTTFB = (
-  onReport: TTFBReportCallbackWithAttribution,
+  onReport: (metric: TTFBMetricWithAttribution) => void,
   opts?: ReportOpts,
 ) => {
-  unattributedOnTTFB(
-    ((metric: TTFBMetricWithAttribution) => {
-      attributeTTFB(metric);
-      onReport(metric);
-    }) as TTFBReportCallback,
-    opts,
-  );
+  unattributedOnTTFB((metric: TTFBMetric) => {
+    attributeTTFB(metric);
+    onReport(metric as TTFBMetricWithAttribution);
+  }, opts);
 };
diff --git a/src/onCLS.ts b/src/onCLS.ts
index ee369752..6f78458b 100644
--- a/src/onCLS.ts
+++ b/src/onCLS.ts
@@ -22,12 +22,7 @@ import {doubleRAF} from './lib/doubleRAF.js';
 import {onHidden} from './lib/onHidden.js';
 import {runOnce} from './lib/runOnce.js';
 import {onFCP} from './onFCP.js';
-import {
-  CLSMetric,
-  CLSReportCallback,
-  MetricRatingThresholds,
-  ReportOpts,
-} from './types.js';
+import {CLSMetric, MetricRatingThresholds, ReportOpts} from './types.js';
 
 /** Thresholds for CLS. See https://web.dev/articles/cls#what_is_a_good_cls_score */
 export const CLSThresholds: MetricRatingThresholds = [0.1, 0.25];
@@ -53,7 +48,10 @@ export const CLSThresholds: MetricRatingThresholds = [0.1, 0.25];
  * hidden. As a result, the `callback` function might be called multiple times
  * during the same page load._
  */
-export const onCLS = (onReport: CLSReportCallback, opts?: ReportOpts) => {
+export const onCLS = (
+  onReport: (metric: CLSMetric) => void,
+  opts?: ReportOpts,
+) => {
   // Set defaults
   opts = opts || {};
 
diff --git a/src/onFCP.ts b/src/onFCP.ts
index 60cfce66..f2a3625a 100644
--- a/src/onFCP.ts
+++ b/src/onFCP.ts
@@ -22,12 +22,7 @@ import {getVisibilityWatcher} from './lib/getVisibilityWatcher.js';
 import {initMetric} from './lib/initMetric.js';
 import {observe} from './lib/observe.js';
 import {whenActivated} from './lib/whenActivated.js';
-import {
-  FCPMetric,
-  FCPReportCallback,
-  MetricRatingThresholds,
-  ReportOpts,
-} from './types.js';
+import {FCPMetric, MetricRatingThresholds, ReportOpts} from './types.js';
 
 /** Thresholds for FCP. See https://web.dev/articles/fcp#what_is_a_good_fcp_score */
 export const FCPThresholds: MetricRatingThresholds = [1800, 3000];
@@ -38,7 +33,10 @@ export const FCPThresholds: MetricRatingThresholds = [1800, 3000];
  * relevant `paint` performance entry used to determine the value. The reported
  * value is a `DOMHighResTimeStamp`.
  */
-export const onFCP = (onReport: FCPReportCallback, opts?: ReportOpts) => {
+export const onFCP = (
+  onReport: (metric: FCPMetric) => void,
+  opts?: ReportOpts,
+) => {
   // Set defaults
   opts = opts || {};
 
@@ -48,7 +46,7 @@ export const onFCP = (onReport: FCPReportCallback, opts?: ReportOpts) => {
     let report: ReturnType<typeof bindReporter>;
 
     const handleEntries = (entries: FCPMetric['entries']) => {
-      (entries as PerformancePaintTiming[]).forEach((entry) => {
+      entries.forEach((entry) => {
         if (entry.name === 'first-contentful-paint') {
           po!.disconnect();
 
diff --git a/src/onFID.ts b/src/onFID.ts
index e3e3c327..cde84b9d 100644
--- a/src/onFID.ts
+++ b/src/onFID.ts
@@ -28,7 +28,6 @@ import {runOnce} from './lib/runOnce.js';
 import {whenActivated} from './lib/whenActivated.js';
 import {
   FIDMetric,
-  FIDReportCallback,
   FirstInputPolyfillCallback,
   MetricRatingThresholds,
   ReportOpts,
@@ -46,7 +45,10 @@ export const FIDThresholds: MetricRatingThresholds = [100, 300];
  * _**Important:** since FID is only reported after the user interacts with the
  * page, it's possible that it will not be reported for some page loads._
  */
-export const onFID = (onReport: FIDReportCallback, opts?: ReportOpts) => {
+export const onFID = (
+  onReport: (metric: FIDMetric) => void,
+  opts?: ReportOpts,
+) => {
   // Set defaults
   opts = opts || {};
 
@@ -65,7 +67,7 @@ export const onFID = (onReport: FIDReportCallback, opts?: ReportOpts) => {
     };
 
     const handleEntries = (entries: FIDMetric['entries']) => {
-      (entries as PerformanceEventTiming[]).forEach(handleEntry);
+      entries.forEach(handleEntry);
     };
 
     const po = observe('first-input', handleEntries);
diff --git a/src/onINP.ts b/src/onINP.ts
index 01cb12b5..f8172872 100644
--- a/src/onINP.ts
+++ b/src/onINP.ts
@@ -28,12 +28,7 @@ import {onHidden} from './lib/onHidden.js';
 import {initInteractionCountPolyfill} from './lib/polyfills/interactionCountPolyfill.js';
 import {whenActivated} from './lib/whenActivated.js';
 
-import {
-  INPMetric,
-  INPReportCallback,
-  MetricRatingThresholds,
-  ReportOpts,
-} from './types.js';
+import {INPMetric, MetricRatingThresholds, ReportOpts} from './types.js';
 
 /** Thresholds for INP. See https://web.dev/articles/inp#what_is_a_good_inp_score */
 export const INPThresholds: MetricRatingThresholds = [200, 500];
@@ -65,7 +60,10 @@ export const INPThresholds: MetricRatingThresholds = [200, 500];
  * hidden. As a result, the `callback` function might be called multiple times
  * during the same page load._
  */
-export const onINP = (onReport: INPReportCallback, opts?: ReportOpts) => {
+export const onINP = (
+  onReport: (metric: INPMetric) => void,
+  opts?: ReportOpts,
+) => {
   // Set defaults
   opts = opts || {};
 
@@ -96,7 +94,7 @@ export const onINP = (onReport: INPReportCallback, opts?: ReportOpts) => {
       // just one or two frames is likely not worth the insight that could be
       // gained.
       durationThreshold: opts!.durationThreshold ?? DEFAULT_DURATION_THRESHOLD,
-    } as PerformanceObserverInit);
+    });
 
     report = bindReporter(
       onReport,
diff --git a/src/onLCP.ts b/src/onLCP.ts
index 622c3638..d88803fe 100644
--- a/src/onLCP.ts
+++ b/src/onLCP.ts
@@ -25,12 +25,7 @@ import {onHidden} from './lib/onHidden.js';
 import {runOnce} from './lib/runOnce.js';
 import {whenActivated} from './lib/whenActivated.js';
 import {whenIdle} from './lib/whenIdle.js';
-import {
-  LCPMetric,
-  MetricRatingThresholds,
-  LCPReportCallback,
-  ReportOpts,
-} from './types.js';
+import {LCPMetric, MetricRatingThresholds, ReportOpts} from './types.js';
 
 /** Thresholds for LCP. See https://web.dev/articles/lcp#what_is_a_good_lcp_score */
 export const LCPThresholds: MetricRatingThresholds = [2500, 4000];
@@ -48,7 +43,10 @@ const reportedMetricIDs: Record<string, boolean> = {};
  * performance entry is dispatched, or once the final value of the metric has
  * been determined.
  */
-export const onLCP = (onReport: LCPReportCallback, opts?: ReportOpts) => {
+export const onLCP = (
+  onReport: (metric: LCPMetric) => void,
+  opts?: ReportOpts,
+) => {
   // Set defaults
   opts = opts || {};
 
@@ -58,7 +56,7 @@ export const onLCP = (onReport: LCPReportCallback, opts?: ReportOpts) => {
     let report: ReturnType<typeof bindReporter>;
 
     const handleEntries = (entries: LCPMetric['entries']) => {
-      const lastEntry = entries[entries.length - 1] as LargestContentfulPaint;
+      const lastEntry = entries[entries.length - 1];
       if (lastEntry) {
         // Only report if the page wasn't hidden prior to LCP.
         if (lastEntry.startTime < visibilityWatcher.firstHiddenTime) {
diff --git a/src/onTTFB.ts b/src/onTTFB.ts
index 5944bfb8..a9c19d98 100644
--- a/src/onTTFB.ts
+++ b/src/onTTFB.ts
@@ -19,11 +19,7 @@ import {initMetric} from './lib/initMetric.js';
 import {isInvalidTimestamp} from './lib/isInvalidTimestamp.js';
 import {onBFCacheRestore} from './lib/bfcache.js';
 import {getNavigationEntry} from './lib/getNavigationEntry.js';
-import {
-  MetricRatingThresholds,
-  ReportOpts,
-  TTFBReportCallback,
-} from './types.js';
+import {MetricRatingThresholds, ReportOpts, TTFBMetric} from './types.js';
 import {getActivationStart} from './lib/getActivationStart.js';
 import {whenActivated} from './lib/whenActivated.js';
 
@@ -60,7 +56,10 @@ const whenReady = (callback: () => void) => {
  * includes time spent on DNS lookup, connection negotiation, network latency,
  * and server processing time.
  */
-export const onTTFB = (onReport: TTFBReportCallback, opts?: ReportOpts) => {
+export const onTTFB = (
+  onReport: (metric: TTFBMetric) => void,
+  opts?: ReportOpts,
+) => {
   // Set defaults
   opts = opts || {};
 
diff --git a/src/types/base.ts b/src/types/base.ts
index 95c0a44f..96806244 100644
--- a/src/types/base.ts
+++ b/src/types/base.ts
@@ -14,14 +14,14 @@
  * limitations under the License.
  */
 
-import type {CLSMetric} from './cls.js';
-import type {FCPMetric} from './fcp.js';
-import type {FIDMetric} from './fid.js';
-import type {INPMetric} from './inp.js';
-import type {LCPMetric} from './lcp.js';
-import type {TTFBMetric} from './ttfb.js';
+import type {CLSMetric, CLSMetricWithAttribution} from './cls.js';
+import type {FCPMetric, FCPMetricWithAttribution} from './fcp.js';
+import type {FIDMetric, FIDMetricWithAttribution} from './fid.js';
+import type {INPMetric, INPMetricWithAttribution} from './inp.js';
+import type {LCPMetric, LCPMetricWithAttribution} from './lcp.js';
+import type {TTFBMetric, TTFBMetricWithAttribution} from './ttfb.js';
 
-export interface Metric {
+export interface MetricBase {
   /**
    * The name of the metric (in acronym form).
    */
@@ -60,7 +60,7 @@ export interface Metric {
    * The array may also be empty if the metric value was not based on any
    * entries (e.g. a CLS value of 0 given no layout shifts).
    */
-  entries: (PerformanceEntry | LayoutShift)[];
+  entries: PerformanceEntry[] | LayoutShift[];
 
   /**
    * The type of navigation.
@@ -92,17 +92,14 @@ export type MetricType =
   | LCPMetric
   | TTFBMetric;
 
-/**
- * A version of the `Metric` that is used with the attribution build.
- */
-export interface MetricWithAttribution extends Metric {
-  /**
-   * An object containing potentially-helpful debugging information that
-   * can be sent along with the metric value for the current page visit in
-   * order to help identify issues happening to real-users in the field.
-   */
-  attribution: {[key: string]: unknown};
-}
+/** The union of supported metric attribution types. */
+export type MetricWithAttribution =
+  | CLSMetricWithAttribution
+  | FCPMetricWithAttribution
+  | FIDMetricWithAttribution
+  | INPMetricWithAttribution
+  | LCPMetricWithAttribution
+  | TTFBMetricWithAttribution;
 
 /**
  * The thresholds of metric's "good", "needs improvement", and "poor" ratings.
@@ -119,10 +116,6 @@ export interface MetricWithAttribution extends Metric {
  */
 export type MetricRatingThresholds = [number, number];
 
-export interface ReportCallback {
-  (metric: MetricType): void;
-}
-
 export interface ReportOpts {
   reportAllChanges?: boolean;
   durationThreshold?: number;
diff --git a/src/types/cls.ts b/src/types/cls.ts
index c3398c5f..5df716c3 100644
--- a/src/types/cls.ts
+++ b/src/types/cls.ts
@@ -14,12 +14,12 @@
  * limitations under the License.
  */
 
-import type {LoadState, Metric} from './base.js';
+import type {LoadState, MetricBase} from './base.js';
 
 /**
  * A CLS-specific version of the Metric object.
  */
-export interface CLSMetric extends Metric {
+export interface CLSMetric extends MetricBase {
   name: 'CLS';
   entries: LayoutShift[];
 }
@@ -72,17 +72,3 @@ export interface CLSAttribution {
 export interface CLSMetricWithAttribution extends CLSMetric {
   attribution: CLSAttribution;
 }
-
-/**
- * A CLS-specific version of the ReportCallback function.
- */
-export interface CLSReportCallback {
-  (metric: CLSMetric): void;
-}
-
-/**
- * A CLS-specific version of the ReportCallback function with attribution.
- */
-export interface CLSReportCallbackWithAttribution {
-  (metric: CLSMetricWithAttribution): void;
-}
diff --git a/src/types/fcp.ts b/src/types/fcp.ts
index 86d48b33..c8660ba6 100644
--- a/src/types/fcp.ts
+++ b/src/types/fcp.ts
@@ -14,12 +14,12 @@
  * limitations under the License.
  */
 
-import type {LoadState, Metric} from './base.js';
+import type {LoadState, MetricBase} from './base.js';
 
 /**
  * An FCP-specific version of the Metric object.
  */
-export interface FCPMetric extends Metric {
+export interface FCPMetric extends MetricBase {
   name: 'FCP';
   entries: PerformancePaintTiming[];
 }
@@ -63,17 +63,3 @@ export interface FCPAttribution {
 export interface FCPMetricWithAttribution extends FCPMetric {
   attribution: FCPAttribution;
 }
-
-/**
- * An FCP-specific version of the ReportCallback function.
- */
-export interface FCPReportCallback {
-  (metric: FCPMetric): void;
-}
-
-/**
- * An FCP-specific version of the ReportCallback function with attribution.
- */
-export interface FCPReportCallbackWithAttribution {
-  (metric: FCPMetricWithAttribution): void;
-}
diff --git a/src/types/fid.ts b/src/types/fid.ts
index f6b71e75..bfa2a2dd 100644
--- a/src/types/fid.ts
+++ b/src/types/fid.ts
@@ -14,12 +14,12 @@
  * limitations under the License.
  */
 
-import type {LoadState, Metric} from './base.js';
+import type {LoadState, MetricBase} from './base.js';
 
 /**
  * An FID-specific version of the Metric object.
  */
-export interface FIDMetric extends Metric {
+export interface FIDMetric extends MetricBase {
   name: 'FID';
   entries: PerformanceEventTiming[];
 }
@@ -63,17 +63,3 @@ export interface FIDAttribution {
 export interface FIDMetricWithAttribution extends FIDMetric {
   attribution: FIDAttribution;
 }
-
-/**
- * An FID-specific version of the ReportCallback function.
- */
-export interface FIDReportCallback {
-  (metric: FIDMetric): void;
-}
-
-/**
- * An FID-specific version of the ReportCallback function with attribution.
- */
-export interface FIDReportCallbackWithAttribution {
-  (metric: FIDMetricWithAttribution): void;
-}
diff --git a/src/types/inp.ts b/src/types/inp.ts
index 039ffb26..95136dc1 100644
--- a/src/types/inp.ts
+++ b/src/types/inp.ts
@@ -14,12 +14,12 @@
  * limitations under the License.
  */
 
-import type {LoadState, Metric} from './base.js';
+import type {LoadState, MetricBase} from './base.js';
 
 /**
  * An INP-specific version of the Metric object.
  */
-export interface INPMetric extends Metric {
+export interface INPMetric extends MetricBase {
   name: 'INP';
   entries: PerformanceEventTiming[];
 }
@@ -122,17 +122,3 @@ export interface INPAttribution {
 export interface INPMetricWithAttribution extends INPMetric {
   attribution: INPAttribution;
 }
-
-/**
- * An INP-specific version of the ReportCallback function.
- */
-export interface INPReportCallback {
-  (metric: INPMetric): void;
-}
-
-/**
- * An INP-specific version of the ReportCallback function with attribution.
- */
-export interface INPReportCallbackWithAttribution {
-  (metric: INPMetricWithAttribution): void;
-}
diff --git a/src/types/lcp.ts b/src/types/lcp.ts
index e5e3b3ef..c90e0c3e 100644
--- a/src/types/lcp.ts
+++ b/src/types/lcp.ts
@@ -14,12 +14,12 @@
  * limitations under the License.
  */
 
-import type {Metric} from './base.js';
+import type {MetricBase} from './base.js';
 
 /**
  * An LCP-specific version of the Metric object.
  */
-export interface LCPMetric extends Metric {
+export interface LCPMetric extends MetricBase {
   name: 'LCP';
   entries: LargestContentfulPaint[];
 }
@@ -86,17 +86,3 @@ export interface LCPAttribution {
 export interface LCPMetricWithAttribution extends LCPMetric {
   attribution: LCPAttribution;
 }
-
-/**
- * An LCP-specific version of the ReportCallback function.
- */
-export interface LCPReportCallback {
-  (metric: LCPMetric): void;
-}
-
-/**
- * An LCP-specific version of the ReportCallback function with attribution.
- */
-export interface LCPReportCallbackWithAttribution {
-  (metric: LCPMetricWithAttribution): void;
-}
diff --git a/src/types/ttfb.ts b/src/types/ttfb.ts
index 2f7097c7..bdf3750b 100644
--- a/src/types/ttfb.ts
+++ b/src/types/ttfb.ts
@@ -14,12 +14,12 @@
  * limitations under the License.
  */
 
-import type {Metric} from './base.js';
+import type {MetricBase} from './base.js';
 
 /**
  * A TTFB-specific version of the Metric object.
  */
-export interface TTFBMetric extends Metric {
+export interface TTFBMetric extends MetricBase {
   name: 'TTFB';
   entries: PerformanceNavigationTiming[];
 }
@@ -76,17 +76,3 @@ export interface TTFBAttribution {
 export interface TTFBMetricWithAttribution extends TTFBMetric {
   attribution: TTFBAttribution;
 }
-
-/**
- * A TTFB-specific version of the ReportCallback function.
- */
-export interface TTFBReportCallback {
-  (metric: TTFBMetric): void;
-}
-
-/**
- * A TTFB-specific version of the ReportCallback function with attribution.
- */
-export interface TTFBReportCallbackWithAttribution {
-  (metric: TTFBMetricWithAttribution): void;
-}

From f563c352771e632794c315d1084f517f2c12d164 Mon Sep 17 00:00:00 2001
From: Brendan Kenny <bckenny@gmail.com>
Date: Wed, 1 May 2024 01:47:47 -0500
Subject: [PATCH 02/14] add attribution in return type

---
 src/attribution/onCLS.ts  | 15 +++++++++------
 src/attribution/onFCP.ts  | 18 +++++++++++-------
 src/attribution/onFID.ts  | 11 +++++++----
 src/attribution/onINP.ts  | 10 ++++++----
 src/attribution/onLCP.ts  | 18 +++++++++++-------
 src/attribution/onTTFB.ts | 15 +++++++++------
 6 files changed, 53 insertions(+), 34 deletions(-)

diff --git a/src/attribution/onCLS.ts b/src/attribution/onCLS.ts
index 5fca98cb..b10c5a82 100644
--- a/src/attribution/onCLS.ts
+++ b/src/attribution/onCLS.ts
@@ -27,13 +27,15 @@ const getLargestLayoutShiftSource = (sources: LayoutShiftAttribution[]) => {
   return sources.find((s) => s.node && s.node.nodeType === 1) || sources[0];
 };
 
-const attributeCLS = (metric: CLSMetric): void => {
+const attributeCLS = (metric: CLSMetric): CLSMetricWithAttribution => {
+  const metricWithAttribution = metric as CLSMetricWithAttribution;
+
   if (metric.entries.length) {
     const largestEntry = getLargestLayoutShiftEntry(metric.entries);
     if (largestEntry && largestEntry.sources && largestEntry.sources.length) {
       const largestSource = getLargestLayoutShiftSource(largestEntry.sources);
       if (largestSource) {
-        (metric as CLSMetricWithAttribution).attribution = {
+        metricWithAttribution.attribution = {
           largestShiftTarget: getSelector(largestSource.node),
           largestShiftTime: largestEntry.startTime,
           largestShiftValue: largestEntry.value,
@@ -41,12 +43,13 @@ const attributeCLS = (metric: CLSMetric): void => {
           largestShiftEntry: largestEntry,
           loadState: getLoadState(largestEntry.startTime),
         };
-        return;
+        return metricWithAttribution;
       }
     }
   }
   // Set an empty object if no other attribution has been set.
-  (metric as CLSMetricWithAttribution).attribution = {};
+  metricWithAttribution.attribution = {};
+  return metricWithAttribution;
 };
 
 /**
@@ -75,7 +78,7 @@ export const onCLS = (
   opts?: ReportOpts,
 ) => {
   unattributedOnCLS((metric: CLSMetric) => {
-    attributeCLS(metric);
-    onReport(metric as CLSMetricWithAttribution);
+    const metricWithAttribution = attributeCLS(metric);
+    onReport(metricWithAttribution);
   }, opts);
 };
diff --git a/src/attribution/onFCP.ts b/src/attribution/onFCP.ts
index 649f96ed..16df0ec7 100644
--- a/src/attribution/onFCP.ts
+++ b/src/attribution/onFCP.ts
@@ -21,34 +21,38 @@ import {isInvalidTimestamp} from '../lib/isInvalidTimestamp.js';
 import {onFCP as unattributedOnFCP} from '../onFCP.js';
 import {FCPMetric, FCPMetricWithAttribution, ReportOpts} from '../types.js';
 
-const attributeFCP = (metric: FCPMetric): void => {
+const attributeFCP = (metric: FCPMetric): FCPMetricWithAttribution => {
+  const metricWithAttribution = metric as FCPMetricWithAttribution;
+
   if (metric.entries.length) {
     const navigationEntry = getNavigationEntry();
     const fcpEntry = metric.entries[metric.entries.length - 1];
 
     if (navigationEntry) {
       const responseStart = navigationEntry.responseStart;
-      if (isInvalidTimestamp(responseStart)) return;
+      // TODO(bckenny): this is wrong.
+      if (isInvalidTimestamp(responseStart)) return metricWithAttribution;
 
       const activationStart = navigationEntry.activationStart || 0;
       const ttfb = Math.max(0, responseStart - activationStart);
 
-      (metric as FCPMetricWithAttribution).attribution = {
+      metricWithAttribution.attribution = {
         timeToFirstByte: ttfb,
         firstByteToFCP: metric.value - ttfb,
         loadState: getLoadState(metric.entries[0].startTime),
         navigationEntry,
         fcpEntry,
       };
-      return;
+      return metricWithAttribution;
     }
   }
   // Set an empty object if no other attribution has been set.
-  (metric as FCPMetricWithAttribution).attribution = {
+  metricWithAttribution.attribution = {
     timeToFirstByte: 0,
     firstByteToFCP: metric.value,
     loadState: getLoadState(getBFCacheRestoreTime()),
   };
+  return metricWithAttribution;
 };
 
 /**
@@ -62,7 +66,7 @@ export const onFCP = (
   opts?: ReportOpts,
 ) => {
   unattributedOnFCP((metric: FCPMetric) => {
-    attributeFCP(metric);
-    onReport(metric as FCPMetricWithAttribution);
+    const metricWithAttribution = attributeFCP(metric);
+    onReport(metricWithAttribution);
   }, opts);
 };
diff --git a/src/attribution/onFID.ts b/src/attribution/onFID.ts
index a75a2577..7a5143e5 100644
--- a/src/attribution/onFID.ts
+++ b/src/attribution/onFID.ts
@@ -19,15 +19,18 @@ import {getSelector} from '../lib/getSelector.js';
 import {onFID as unattributedOnFID} from '../onFID.js';
 import {FIDMetric, FIDMetricWithAttribution, ReportOpts} from '../types.js';
 
-const attributeFID = (metric: FIDMetric): void => {
+const attributeFID = (metric: FIDMetric): FIDMetricWithAttribution => {
+  const metricWithAttribution = metric as FIDMetricWithAttribution;
+
   const fidEntry = metric.entries[0];
-  (metric as FIDMetricWithAttribution).attribution = {
+  metricWithAttribution.attribution = {
     eventTarget: getSelector(fidEntry.target),
     eventType: fidEntry.name,
     eventTime: fidEntry.startTime,
     eventEntry: fidEntry,
     loadState: getLoadState(fidEntry.startTime),
   };
+  return metricWithAttribution;
 };
 
 /**
@@ -44,7 +47,7 @@ export const onFID = (
   opts?: ReportOpts,
 ) => {
   unattributedOnFID((metric: FIDMetric) => {
-    attributeFID(metric);
-    onReport(metric as FIDMetricWithAttribution);
+    const metricWithAttribution = attributeFID(metric);
+    onReport(metricWithAttribution);
   }, opts);
 };
diff --git a/src/attribution/onINP.ts b/src/attribution/onINP.ts
index 378ad2c2..e1983303 100644
--- a/src/attribution/onINP.ts
+++ b/src/attribution/onINP.ts
@@ -186,7 +186,7 @@ const getIntersectingLoAFs = (
   return intersectingLoAFs;
 };
 
-const attributeINP = (metric: INPMetric): void => {
+const attributeINP = (metric: INPMetric): INPMetricWithAttribution => {
   const firstEntry = metric.entries[0];
   const renderTime = entryToRenderTimeMap.get(firstEntry)!;
   const group = pendingEntriesGroupMap.get(renderTime)!;
@@ -220,7 +220,8 @@ const attributeINP = (metric: INPMetric): void => {
 
   const nextPaintTime = Math.max.apply(Math, nextPaintTimeCandidates);
 
-  (metric as INPMetricWithAttribution).attribution = {
+  const metricWithAttribution = metric as INPMetricWithAttribution;
+  metricWithAttribution.attribution = {
     interactionTarget: getSelector(
       firstEntryWithTarget && firstEntryWithTarget.target,
     ),
@@ -234,6 +235,7 @@ const attributeINP = (metric: INPMetric): void => {
     presentationDelay: Math.max(nextPaintTime - processingEnd, 0),
     loadState: getLoadState(firstEntry.startTime),
   };
+  return metricWithAttribution;
 };
 
 /**
@@ -278,8 +280,8 @@ export const onINP = (
     // running in Chrome (EventTimingKeypressAndCompositionInteractionId)
     // 123+ that if rolled out fully would make this no longer necessary.
     whenIdle(() => {
-      attributeINP(metric);
-      onReport(metric as INPMetricWithAttribution);
+      const metricWithAttribution = attributeINP(metric);
+      onReport(metricWithAttribution);
     });
   }, opts);
 };
diff --git a/src/attribution/onLCP.ts b/src/attribution/onLCP.ts
index aeba48fb..3e5b21b7 100644
--- a/src/attribution/onLCP.ts
+++ b/src/attribution/onLCP.ts
@@ -25,13 +25,16 @@ import {
   ReportOpts,
 } from '../types.js';
 
-const attributeLCP = (metric: LCPMetric) => {
+const attributeLCP = (metric: LCPMetric): LCPMetricWithAttribution => {
+  const metricWithAttribution = metric as LCPMetricWithAttribution;
+
   if (metric.entries.length) {
     const navigationEntry = getNavigationEntry();
 
     if (navigationEntry) {
       const responseStart = navigationEntry.responseStart;
-      if (isInvalidTimestamp(responseStart)) return;
+      // TODO(bckenny): this is wrong.
+      if (isInvalidTimestamp(responseStart)) return metricWithAttribution;
 
       const activationStart = navigationEntry.activationStart || 0;
       const lcpEntry = metric.entries[metric.entries.length - 1];
@@ -78,17 +81,18 @@ const attributeLCP = (metric: LCPMetric) => {
         attribution.lcpResourceEntry = lcpResourceEntry;
       }
 
-      (metric as LCPMetricWithAttribution).attribution = attribution;
-      return;
+      metricWithAttribution.attribution = attribution;
+      return metricWithAttribution;
     }
   }
   // Set an empty object if no other attribution has been set.
-  (metric as LCPMetricWithAttribution).attribution = {
+  metricWithAttribution.attribution = {
     timeToFirstByte: 0,
     resourceLoadDelay: 0,
     resourceLoadDuration: 0,
     elementRenderDelay: metric.value,
   };
+  return metricWithAttribution;
 };
 
 /**
@@ -107,7 +111,7 @@ export const onLCP = (
   opts?: ReportOpts,
 ) => {
   unattributedOnLCP((metric: LCPMetric) => {
-    attributeLCP(metric);
-    onReport(metric as LCPMetricWithAttribution);
+    const metricWithAttribution = attributeLCP(metric);
+    onReport(metricWithAttribution);
   }, opts);
 };
diff --git a/src/attribution/onTTFB.ts b/src/attribution/onTTFB.ts
index 3f267c04..51c92a46 100644
--- a/src/attribution/onTTFB.ts
+++ b/src/attribution/onTTFB.ts
@@ -17,7 +17,9 @@
 import {onTTFB as unattributedOnTTFB} from '../onTTFB.js';
 import {TTFBMetric, TTFBMetricWithAttribution, ReportOpts} from '../types.js';
 
-const attributeTTFB = (metric: TTFBMetric): void => {
+const attributeTTFB = (metric: TTFBMetric): TTFBMetricWithAttribution => {
+  const metricWithAttribution = metric as TTFBMetricWithAttribution;
+
   if (metric.entries.length) {
     const navigationEntry = metric.entries[0];
     const activationStart = navigationEntry.activationStart || 0;
@@ -43,7 +45,7 @@ const attributeTTFB = (metric: TTFBMetric): void => {
       0,
     );
 
-    (metric as TTFBMetricWithAttribution).attribution = {
+    metricWithAttribution.attribution = {
       waitingDuration: waitEnd,
       cacheDuration: dnsStart - waitEnd,
       // dnsEnd usually equals connectStart but use connectStart over dnsEnd
@@ -57,16 +59,17 @@ const attributeTTFB = (metric: TTFBMetric): void => {
       requestDuration: metric.value - connectEnd,
       navigationEntry: navigationEntry,
     };
-    return;
+    return metricWithAttribution;
   }
   // Set an empty object if no other attribution has been set.
-  (metric as TTFBMetricWithAttribution).attribution = {
+  metricWithAttribution.attribution = {
     waitingDuration: 0,
     cacheDuration: 0,
     dnsDuration: 0,
     connectionDuration: 0,
     requestDuration: 0,
   };
+  return metricWithAttribution;
 };
 
 /**
@@ -89,7 +92,7 @@ export const onTTFB = (
   opts?: ReportOpts,
 ) => {
   unattributedOnTTFB((metric: TTFBMetric) => {
-    attributeTTFB(metric);
-    onReport(metric as TTFBMetricWithAttribution);
+    const metricWithAttribution = attributeTTFB(metric);
+    onReport(metricWithAttribution);
   }, opts);
 };

From 06550521307dbe4f3a3ba4550d47cf6535a41c02 Mon Sep 17 00:00:00 2001
From: Brendan Kenny <bckenny@gmail.com>
Date: Wed, 1 May 2024 18:09:35 -0500
Subject: [PATCH 03/14] revert Metric name

---
 src/types/base.ts | 4 ++--
 src/types/cls.ts  | 4 ++--
 src/types/fcp.ts  | 4 ++--
 src/types/fid.ts  | 4 ++--
 src/types/inp.ts  | 4 ++--
 src/types/lcp.ts  | 4 ++--
 src/types/ttfb.ts | 4 ++--
 7 files changed, 14 insertions(+), 14 deletions(-)

diff --git a/src/types/base.ts b/src/types/base.ts
index 96806244..9d574e90 100644
--- a/src/types/base.ts
+++ b/src/types/base.ts
@@ -21,7 +21,7 @@ import type {INPMetric, INPMetricWithAttribution} from './inp.js';
 import type {LCPMetric, LCPMetricWithAttribution} from './lcp.js';
 import type {TTFBMetric, TTFBMetricWithAttribution} from './ttfb.js';
 
-export interface MetricBase {
+export interface Metric {
   /**
    * The name of the metric (in acronym form).
    */
@@ -60,7 +60,7 @@ export interface MetricBase {
    * The array may also be empty if the metric value was not based on any
    * entries (e.g. a CLS value of 0 given no layout shifts).
    */
-  entries: PerformanceEntry[] | LayoutShift[];
+  entries: PerformanceEntry[];
 
   /**
    * The type of navigation.
diff --git a/src/types/cls.ts b/src/types/cls.ts
index 5df716c3..c79ce4c0 100644
--- a/src/types/cls.ts
+++ b/src/types/cls.ts
@@ -14,12 +14,12 @@
  * limitations under the License.
  */
 
-import type {LoadState, MetricBase} from './base.js';
+import type {LoadState, Metric} from './base.js';
 
 /**
  * A CLS-specific version of the Metric object.
  */
-export interface CLSMetric extends MetricBase {
+export interface CLSMetric extends Metric {
   name: 'CLS';
   entries: LayoutShift[];
 }
diff --git a/src/types/fcp.ts b/src/types/fcp.ts
index c8660ba6..ef599b34 100644
--- a/src/types/fcp.ts
+++ b/src/types/fcp.ts
@@ -14,12 +14,12 @@
  * limitations under the License.
  */
 
-import type {LoadState, MetricBase} from './base.js';
+import type {LoadState, Metric} from './base.js';
 
 /**
  * An FCP-specific version of the Metric object.
  */
-export interface FCPMetric extends MetricBase {
+export interface FCPMetric extends Metric {
   name: 'FCP';
   entries: PerformancePaintTiming[];
 }
diff --git a/src/types/fid.ts b/src/types/fid.ts
index bfa2a2dd..5b2dcba3 100644
--- a/src/types/fid.ts
+++ b/src/types/fid.ts
@@ -14,12 +14,12 @@
  * limitations under the License.
  */
 
-import type {LoadState, MetricBase} from './base.js';
+import type {LoadState, Metric} from './base.js';
 
 /**
  * An FID-specific version of the Metric object.
  */
-export interface FIDMetric extends MetricBase {
+export interface FIDMetric extends Metric {
   name: 'FID';
   entries: PerformanceEventTiming[];
 }
diff --git a/src/types/inp.ts b/src/types/inp.ts
index 95136dc1..d469be47 100644
--- a/src/types/inp.ts
+++ b/src/types/inp.ts
@@ -14,12 +14,12 @@
  * limitations under the License.
  */
 
-import type {LoadState, MetricBase} from './base.js';
+import type {LoadState, Metric} from './base.js';
 
 /**
  * An INP-specific version of the Metric object.
  */
-export interface INPMetric extends MetricBase {
+export interface INPMetric extends Metric {
   name: 'INP';
   entries: PerformanceEventTiming[];
 }
diff --git a/src/types/lcp.ts b/src/types/lcp.ts
index c90e0c3e..4761fdd1 100644
--- a/src/types/lcp.ts
+++ b/src/types/lcp.ts
@@ -14,12 +14,12 @@
  * limitations under the License.
  */
 
-import type {MetricBase} from './base.js';
+import type {Metric} from './base.js';
 
 /**
  * An LCP-specific version of the Metric object.
  */
-export interface LCPMetric extends MetricBase {
+export interface LCPMetric extends Metric {
   name: 'LCP';
   entries: LargestContentfulPaint[];
 }
diff --git a/src/types/ttfb.ts b/src/types/ttfb.ts
index bdf3750b..3559084d 100644
--- a/src/types/ttfb.ts
+++ b/src/types/ttfb.ts
@@ -14,12 +14,12 @@
  * limitations under the License.
  */
 
-import type {MetricBase} from './base.js';
+import type {Metric} from './base.js';
 
 /**
  * A TTFB-specific version of the Metric object.
  */
-export interface TTFBMetric extends MetricBase {
+export interface TTFBMetric extends Metric {
   name: 'TTFB';
   entries: PerformanceNavigationTiming[];
 }

From 535b34e2edee258427f64a3f005a70f09686a023 Mon Sep 17 00:00:00 2001
From: Brendan Kenny <bckenny@gmail.com>
Date: Wed, 1 May 2024 19:14:18 -0500
Subject: [PATCH 04/14] attribution object

---
 src/attribution/onCLS.ts  | 19 +++++++++++-----
 src/attribution/onFCP.ts  | 48 ++++++++++++++++++++++-----------------
 src/attribution/onFID.ts  | 15 ++++++++----
 src/attribution/onINP.ts  | 14 +++++++++---
 src/attribution/onLCP.ts  | 36 +++++++++++++----------------
 src/attribution/onTTFB.ts | 31 +++++++++++++++----------
 6 files changed, 97 insertions(+), 66 deletions(-)

diff --git a/src/attribution/onCLS.ts b/src/attribution/onCLS.ts
index b10c5a82..abd0d0cf 100644
--- a/src/attribution/onCLS.ts
+++ b/src/attribution/onCLS.ts
@@ -17,7 +17,12 @@
 import {getLoadState} from '../lib/getLoadState.js';
 import {getSelector} from '../lib/getSelector.js';
 import {onCLS as unattributedOnCLS} from '../onCLS.js';
-import {CLSMetric, CLSMetricWithAttribution, ReportOpts} from '../types.js';
+import {
+  CLSAttribution,
+  CLSMetric,
+  CLSMetricWithAttribution,
+  ReportOpts,
+} from '../types.js';
 
 const getLargestLayoutShiftEntry = (entries: LayoutShift[]) => {
   return entries.reduce((a, b) => (a && a.value > b.value ? a : b));
@@ -28,14 +33,15 @@ const getLargestLayoutShiftSource = (sources: LayoutShiftAttribution[]) => {
 };
 
 const attributeCLS = (metric: CLSMetric): CLSMetricWithAttribution => {
-  const metricWithAttribution = metric as CLSMetricWithAttribution;
+  // Use an empty object if no other attribution has been set.
+  let attribution: CLSAttribution = {};
 
   if (metric.entries.length) {
     const largestEntry = getLargestLayoutShiftEntry(metric.entries);
     if (largestEntry && largestEntry.sources && largestEntry.sources.length) {
       const largestSource = getLargestLayoutShiftSource(largestEntry.sources);
       if (largestSource) {
-        metricWithAttribution.attribution = {
+        attribution = {
           largestShiftTarget: getSelector(largestSource.node),
           largestShiftTime: largestEntry.startTime,
           largestShiftValue: largestEntry.value,
@@ -43,12 +49,13 @@ const attributeCLS = (metric: CLSMetric): CLSMetricWithAttribution => {
           largestShiftEntry: largestEntry,
           loadState: getLoadState(largestEntry.startTime),
         };
-        return metricWithAttribution;
       }
     }
   }
-  // Set an empty object if no other attribution has been set.
-  metricWithAttribution.attribution = {};
+
+  // Cast to attribution metric so it can be populated.
+  const metricWithAttribution = metric as CLSMetricWithAttribution;
+  metricWithAttribution.attribution = attribution;
   return metricWithAttribution;
 };
 
diff --git a/src/attribution/onFCP.ts b/src/attribution/onFCP.ts
index 16df0ec7..78790169 100644
--- a/src/attribution/onFCP.ts
+++ b/src/attribution/onFCP.ts
@@ -19,10 +19,20 @@ import {getLoadState} from '../lib/getLoadState.js';
 import {getNavigationEntry} from '../lib/getNavigationEntry.js';
 import {isInvalidTimestamp} from '../lib/isInvalidTimestamp.js';
 import {onFCP as unattributedOnFCP} from '../onFCP.js';
-import {FCPMetric, FCPMetricWithAttribution, ReportOpts} from '../types.js';
+import {
+  FCPAttribution,
+  FCPMetric,
+  FCPMetricWithAttribution,
+  ReportOpts,
+} from '../types.js';
 
 const attributeFCP = (metric: FCPMetric): FCPMetricWithAttribution => {
-  const metricWithAttribution = metric as FCPMetricWithAttribution;
+  // Use a default object if no other attribution has been set.
+  let attribution: FCPAttribution = {
+    timeToFirstByte: 0,
+    firstByteToFCP: metric.value,
+    loadState: getLoadState(getBFCacheRestoreTime()),
+  };
 
   if (metric.entries.length) {
     const navigationEntry = getNavigationEntry();
@@ -30,28 +40,24 @@ const attributeFCP = (metric: FCPMetric): FCPMetricWithAttribution => {
 
     if (navigationEntry) {
       const responseStart = navigationEntry.responseStart;
-      // TODO(bckenny): this is wrong.
-      if (isInvalidTimestamp(responseStart)) return metricWithAttribution;
-
-      const activationStart = navigationEntry.activationStart || 0;
-      const ttfb = Math.max(0, responseStart - activationStart);
+      if (!isInvalidTimestamp(responseStart)) {
+        const activationStart = navigationEntry.activationStart || 0;
+        const ttfb = Math.max(0, responseStart - activationStart);
 
-      metricWithAttribution.attribution = {
-        timeToFirstByte: ttfb,
-        firstByteToFCP: metric.value - ttfb,
-        loadState: getLoadState(metric.entries[0].startTime),
-        navigationEntry,
-        fcpEntry,
-      };
-      return metricWithAttribution;
+        attribution = {
+          timeToFirstByte: ttfb,
+          firstByteToFCP: metric.value - ttfb,
+          loadState: getLoadState(metric.entries[0].startTime),
+          navigationEntry,
+          fcpEntry,
+        };
+      }
     }
   }
-  // Set an empty object if no other attribution has been set.
-  metricWithAttribution.attribution = {
-    timeToFirstByte: 0,
-    firstByteToFCP: metric.value,
-    loadState: getLoadState(getBFCacheRestoreTime()),
-  };
+
+  // Cast to attribution metric so it can be populated.
+  const metricWithAttribution = metric as FCPMetricWithAttribution;
+  metricWithAttribution.attribution = attribution;
   return metricWithAttribution;
 };
 
diff --git a/src/attribution/onFID.ts b/src/attribution/onFID.ts
index 7a5143e5..9dcfd6dc 100644
--- a/src/attribution/onFID.ts
+++ b/src/attribution/onFID.ts
@@ -17,19 +17,26 @@
 import {getLoadState} from '../lib/getLoadState.js';
 import {getSelector} from '../lib/getSelector.js';
 import {onFID as unattributedOnFID} from '../onFID.js';
-import {FIDMetric, FIDMetricWithAttribution, ReportOpts} from '../types.js';
+import {
+  FIDAttribution,
+  FIDMetric,
+  FIDMetricWithAttribution,
+  ReportOpts,
+} from '../types.js';
 
 const attributeFID = (metric: FIDMetric): FIDMetricWithAttribution => {
-  const metricWithAttribution = metric as FIDMetricWithAttribution;
-
   const fidEntry = metric.entries[0];
-  metricWithAttribution.attribution = {
+  const attribution: FIDAttribution = {
     eventTarget: getSelector(fidEntry.target),
     eventType: fidEntry.name,
     eventTime: fidEntry.startTime,
     eventEntry: fidEntry,
     loadState: getLoadState(fidEntry.startTime),
   };
+
+  // Cast to attribution metric so it can be populated.
+  const metricWithAttribution = metric as FIDMetricWithAttribution;
+  metricWithAttribution.attribution = attribution;
   return metricWithAttribution;
 };
 
diff --git a/src/attribution/onINP.ts b/src/attribution/onINP.ts
index e1983303..91aba61d 100644
--- a/src/attribution/onINP.ts
+++ b/src/attribution/onINP.ts
@@ -23,7 +23,12 @@ import {
 import {observe} from '../lib/observe.js';
 import {whenIdle} from '../lib/whenIdle.js';
 import {onINP as unattributedOnINP} from '../onINP.js';
-import {INPMetric, INPMetricWithAttribution, ReportOpts} from '../types.js';
+import {
+  INPAttribution,
+  INPMetric,
+  INPMetricWithAttribution,
+  ReportOpts,
+} from '../types.js';
 
 interface pendingEntriesGroup {
   startTime: DOMHighResTimeStamp;
@@ -220,8 +225,7 @@ const attributeINP = (metric: INPMetric): INPMetricWithAttribution => {
 
   const nextPaintTime = Math.max.apply(Math, nextPaintTimeCandidates);
 
-  const metricWithAttribution = metric as INPMetricWithAttribution;
-  metricWithAttribution.attribution = {
+  const attribution: INPAttribution = {
     interactionTarget: getSelector(
       firstEntryWithTarget && firstEntryWithTarget.target,
     ),
@@ -235,6 +239,10 @@ const attributeINP = (metric: INPMetric): INPMetricWithAttribution => {
     presentationDelay: Math.max(nextPaintTime - processingEnd, 0),
     loadState: getLoadState(firstEntry.startTime),
   };
+
+  // Cast to attribution metric so it can be populated.
+  const metricWithAttribution = metric as INPMetricWithAttribution;
+  metricWithAttribution.attribution = attribution;
   return metricWithAttribution;
 };
 
diff --git a/src/attribution/onLCP.ts b/src/attribution/onLCP.ts
index 3e5b21b7..cdf56596 100644
--- a/src/attribution/onLCP.ts
+++ b/src/attribution/onLCP.ts
@@ -26,16 +26,18 @@ import {
 } from '../types.js';
 
 const attributeLCP = (metric: LCPMetric): LCPMetricWithAttribution => {
-  const metricWithAttribution = metric as LCPMetricWithAttribution;
-
-  if (metric.entries.length) {
-    const navigationEntry = getNavigationEntry();
-
-    if (navigationEntry) {
-      const responseStart = navigationEntry.responseStart;
-      // TODO(bckenny): this is wrong.
-      if (isInvalidTimestamp(responseStart)) return metricWithAttribution;
+  // Use a default object if no other attribution has been set.
+  let attribution: LCPAttribution = {
+    timeToFirstByte: 0,
+    resourceLoadDelay: 0,
+    resourceLoadDuration: 0,
+    elementRenderDelay: metric.value,
+  };
 
+  const navigationEntry = getNavigationEntry();
+  if (metric.entries.length && navigationEntry) {
+    const responseStart = navigationEntry.responseStart;
+    if (!isInvalidTimestamp(responseStart)) {
       const activationStart = navigationEntry.activationStart || 0;
       const lcpEntry = metric.entries[metric.entries.length - 1];
       const lcpResourceEntry =
@@ -63,7 +65,7 @@ const attributeLCP = (metric: LCPMetric): LCPMetricWithAttribution => {
         lcpEntry.startTime - activationStart,
       );
 
-      const attribution: LCPAttribution = {
+      attribution = {
         element: getSelector(lcpEntry.element),
         timeToFirstByte: ttfb,
         resourceLoadDelay: lcpRequestStart - ttfb,
@@ -80,18 +82,12 @@ const attributeLCP = (metric: LCPMetric): LCPMetricWithAttribution => {
       if (lcpResourceEntry) {
         attribution.lcpResourceEntry = lcpResourceEntry;
       }
-
-      metricWithAttribution.attribution = attribution;
-      return metricWithAttribution;
     }
   }
-  // Set an empty object if no other attribution has been set.
-  metricWithAttribution.attribution = {
-    timeToFirstByte: 0,
-    resourceLoadDelay: 0,
-    resourceLoadDuration: 0,
-    elementRenderDelay: metric.value,
-  };
+
+  // Cast to attribution metric so it can be populated.
+  const metricWithAttribution = metric as LCPMetricWithAttribution;
+  metricWithAttribution.attribution = attribution;
   return metricWithAttribution;
 };
 
diff --git a/src/attribution/onTTFB.ts b/src/attribution/onTTFB.ts
index 51c92a46..3c1529b8 100644
--- a/src/attribution/onTTFB.ts
+++ b/src/attribution/onTTFB.ts
@@ -15,10 +15,22 @@
  */
 
 import {onTTFB as unattributedOnTTFB} from '../onTTFB.js';
-import {TTFBMetric, TTFBMetricWithAttribution, ReportOpts} from '../types.js';
+import {
+  TTFBMetric,
+  TTFBMetricWithAttribution,
+  ReportOpts,
+  TTFBAttribution,
+} from '../types.js';
 
 const attributeTTFB = (metric: TTFBMetric): TTFBMetricWithAttribution => {
-  const metricWithAttribution = metric as TTFBMetricWithAttribution;
+  // Use a default object if no other attribution has been set.
+  let attribution: TTFBAttribution = {
+    waitingDuration: 0,
+    cacheDuration: 0,
+    dnsDuration: 0,
+    connectionDuration: 0,
+    requestDuration: 0,
+  };
 
   if (metric.entries.length) {
     const navigationEntry = metric.entries[0];
@@ -45,7 +57,7 @@ const attributeTTFB = (metric: TTFBMetric): TTFBMetricWithAttribution => {
       0,
     );
 
-    metricWithAttribution.attribution = {
+    attribution = {
       waitingDuration: waitEnd,
       cacheDuration: dnsStart - waitEnd,
       // dnsEnd usually equals connectStart but use connectStart over dnsEnd
@@ -59,16 +71,11 @@ const attributeTTFB = (metric: TTFBMetric): TTFBMetricWithAttribution => {
       requestDuration: metric.value - connectEnd,
       navigationEntry: navigationEntry,
     };
-    return metricWithAttribution;
   }
-  // Set an empty object if no other attribution has been set.
-  metricWithAttribution.attribution = {
-    waitingDuration: 0,
-    cacheDuration: 0,
-    dnsDuration: 0,
-    connectionDuration: 0,
-    requestDuration: 0,
-  };
+
+  // Cast to attribution metric so it can be populated.
+  const metricWithAttribution = metric as TTFBMetricWithAttribution;
+  metricWithAttribution.attribution = attribution;
   return metricWithAttribution;
 };
 

From b7a54f1483029f15fe5e8b5e30c7768875aa2f56 Mon Sep 17 00:00:00 2001
From: Brendan Kenny <bckenny@gmail.com>
Date: Thu, 2 May 2024 00:06:33 -0500
Subject: [PATCH 05/14] update readme

---
 README.md | 159 +++++++++++++++++++++++++++---------------------------
 1 file changed, 80 insertions(+), 79 deletions(-)

diff --git a/README.md b/README.md
index c7daf3f9..646246df 100644
--- a/README.md
+++ b/README.md
@@ -100,7 +100,7 @@ To load the "attribution" build, change any `import` statements that reference `
 + import {onLCP, onINP, onCLS} from 'web-vitals/attribution';
 ```
 
-Usage for each of the imported function is identical to the standard build, but when importing from the attribution build, the [`Metric`](#metric) object will contain an additional [`attribution`](#metricwithattribution) property.
+Usage for each of the imported function is identical to the standard build, but when importing from the attribution build, the [metrics](#metrics) objects will contain an additional [`attribution`](#attribution) property.
 
 See [Send attribution data](#send-attribution-data) for usage examples, and the [`attribution` reference](#attribution) for details on what values are added for each metric.
 
@@ -488,17 +488,70 @@ For guidance on how to collect and use real-user data to debug performance issue
 
 ## API
 
-### Types:
+### Types
 
-#### `Metric`
+#### Metrics
+
+##### [`CLSMetric`](/src/types/cls.ts#:~:text=interface%20CLSMetric)
 
 ```ts
-interface Metric {
-  /**
-   * The name of the metric (in acronym form).
-   */
-  name: 'CLS' | 'FCP' | 'FID' | 'INP' | 'LCP' | 'TTFB';
+interface CLSMetric extends Metric {
+  name: 'CLS';
+  entries: LayoutShift[];
+}
+```
+
+##### [`FCPMetric`](/src/types/fcp.ts#:~:text=interface%20FCPMetric)
+
+```ts
+interface FCPMetric extends Metric {
+  name: 'FCP';
+  entries: PerformancePaintTiming[];
+}
+```
+
+##### [`FIDMetric`](/src/types/fid.ts#:~:text=interface%20FIDMetric)
+
+```ts
+interface FIDMetric extends Metric {
+  name: 'FID';
+  entries: PerformanceEventTiming[];
+}
+```
+
+##### [`INPMetric`](/src/types/inp.ts#:~:text=interface%20INPMetric)
+
+```ts
+interface INPMetric extends Metric {
+  name: 'INP';
+  entries: PerformanceEventTiming[];
+}
+```
 
+##### [`LCPMetric`](/src/types/lcp.ts#:~:text=interface%20LCPMetric)
+
+```ts
+interface LCPMetric extends Metric {
+  name: 'LCP';
+  entries: LargestContentfulPaint[];
+}
+```
+
+##### [`TTFBMetric`](/src/types/ttfb.ts#:~:text=interface%20TTFBMetric)
+
+```ts
+interface TTFBMetric extends Metric {
+  name: 'TTFB';
+  entries: PerformanceNavigationTiming[];
+}
+```
+
+##### `Metric`
+
+All metrics share the following properties:
+
+```ts
+interface Metric {
   /**
    * The current value of the metric.
    */
@@ -527,13 +580,6 @@ interface Metric {
    */
   id: string;
 
-  /**
-   * Any performance entries relevant to the metric value calculation.
-   * The array may also be empty if the metric value was not based on any
-   * entries (e.g. a CLS value of 0 given no layout shifts).
-   */
-  entries: (PerformanceEntry | LayoutShift)[];
-
   /**
    * The type of navigation.
    *
@@ -556,39 +602,6 @@ interface Metric {
 }
 ```
 
-Metric-specific subclasses:
-
-- [`CLSMetric`](/src/types/cls.ts#:~:text=interface%20CLSMetric)
-- [`FCPMetric`](/src/types/fcp.ts#:~:text=interface%20FCPMetric)
-- [`FIDMetric`](/src/types/fid.ts#:~:text=interface%20FIDMetric)
-- [`INPMetric`](/src/types/inp.ts#:~:text=interface%20INPMetric)
-- [`LCPMetric`](/src/types/lcp.ts#:~:text=interface%20LCPMetric)
-- [`TTFBMetric`](/src/types/ttfb.ts#:~:text=interface%20TTFBMetric)
-
-#### `MetricWithAttribution`
-
-See the [attribution build](#attribution-build) section for details on how to use this feature.
-
-```ts
-interface MetricWithAttribution extends Metric {
-  /**
-   * An object containing potentially-helpful debugging information that
-   * can be sent along with the metric value for the current page visit in
-   * order to help identify issues happening to real-users in the field.
-   */
-  attribution: {[key: string]: unknown};
-}
-```
-
-Metric-specific subclasses:
-
-- [`CLSMetricWithAttribution`](/src/types/cls.ts#:~:text=interface%20CLSMetricWithAttribution)
-- [`FCPMetricWithAttribution`](/src/types/fcp.ts#:~:text=interface%20FCPMetricWithAttribution)
-- [`FIDMetricWithAttribution`](/src/types/fid.ts#:~:text=interface%20FIDMetricWithAttribution)
-- [`INPMetricWithAttribution`](/src/types/inp.ts#:~:text=interface%20INPMetricWithAttribution)
-- [`LCPMetricWithAttribution`](/src/types/lcp.ts#:~:text=interface%20LCPMetricWithAttribution)
-- [`TTFBMetricWithAttribution`](/src/types/ttfb.ts#:~:text=interface%20TTFBMetricWithAttribution)
-
 #### `MetricRatingThresholds`
 
 The thresholds of metric's "good", "needs improvement", and "poor" ratings.
@@ -604,28 +617,11 @@ The thresholds of metric's "good", "needs improvement", and "poor" ratings.
 | > [1]           | "poor"              |
 
 ```ts
-export type MetricRatingThresholds = [number, number];
+type MetricRatingThresholds = [number, number];
 ```
 
 _See also [Rating Thresholds](#rating-thresholds)._
 
-#### `ReportCallback`
-
-```ts
-interface ReportCallback {
-  (metric: Metric): void;
-}
-```
-
-Metric-specific subclasses:
-
-- [`CLSReportCallback`](/src/types/cls.ts#:~:text=interface%20CLSReportCallback)
-- [`FCPReportCallback`](/src/types/fcp.ts#:~:text=interface%20FCPReportCallback)
-- [`FIDReportCallback`](/src/types/fid.ts#:~:text=interface%20FIDReportCallback)
-- [`INPReportCallback`](/src/types/inp.ts#:~:text=interface%20INPReportCallback)
-- [`LCPReportCallback`](/src/types/lcp.ts#:~:text=interface%20LCPReportCallback)
-- [`TTFBReportCallback`](/src/types/ttfb.ts#:~:text=interface%20TTFBReportCallback)
-
 #### `ReportOpts`
 
 ```ts
@@ -667,7 +663,7 @@ type LoadState =
 #### `onCLS()`
 
 ```ts
-type onCLS = (callback: CLSReportCallback, opts?: ReportOpts) => void;
+function onCLS(callback: (metric: CLSMetric) => void, opts?: ReportOpts): void;
 ```
 
 Calculates the [CLS](https://web.dev/articles/cls) value for the current page and calls the `callback` function once the value is ready to be reported, along with all `layout-shift` performance entries that were used in the metric value calculation. The reported value is a [double](https://heycam.github.io/webidl/#idl-double) (corresponding to a [layout shift score](https://web.dev/articles/cls#layout_shift_score)).
@@ -679,7 +675,7 @@ _**Important:** CLS should be continually monitored for changes throughout the e
 #### `onFCP()`
 
 ```ts
-type onFCP = (callback: FCPReportCallback, opts?: ReportOpts) => void;
+function onFCP(callback: (metric: FCPMetric) => void, opts?: ReportOpts): void;
 ```
 
 Calculates the [FCP](https://web.dev/articles/fcp) value for the current page and calls the `callback` function once the value is ready, along with the relevant `paint` performance entry used to determine the value. The reported value is a [`DOMHighResTimeStamp`](https://developer.mozilla.org/docs/Web/API/DOMHighResTimeStamp).
@@ -689,7 +685,7 @@ Calculates the [FCP](https://web.dev/articles/fcp) value for the current page an
 _Deprecated and will be removed in next major release_
 
 ```ts
-type onFID = (callback: FIDReportCallback, opts?: ReportOpts) => void;
+function onFID(callback: (metric: FIDMetric) => void, opts?: ReportOpts): void;
 ```
 
 Calculates the [FID](https://web.dev/articles/fid) value for the current page and calls the `callback` function once the value is ready, along with the relevant `first-input` performance entry used to determine the value. The reported value is a [`DOMHighResTimeStamp`](https://developer.mozilla.org/docs/Web/API/DOMHighResTimeStamp).
@@ -699,7 +695,7 @@ _**Important:** since FID is only reported after the user interacts with the pag
 #### `onINP()`
 
 ```ts
-type onINP = (callback: INPReportCallback, opts?: ReportOpts) => void;
+function onINP(callback: (metric: INPMetric) => void, opts?: ReportOpts): void;
 ```
 
 Calculates the [INP](https://web.dev/articles/inp) value for the current page and calls the `callback` function once the value is ready, along with the `event` performance entries reported for that interaction. The reported value is a [`DOMHighResTimeStamp`](https://developer.mozilla.org/docs/Web/API/DOMHighResTimeStamp).
@@ -713,7 +709,7 @@ _**Important:** INP should be continually monitored for changes throughout the e
 #### `onLCP()`
 
 ```ts
-type onLCP = (callback: LCPReportCallback, opts?: ReportOpts) => void;
+function onLCP(callback: (metric: LCPMetric) => void, opts?: ReportOpts): void;
 ```
 
 Calculates the [LCP](https://web.dev/articles/lcp) value for the current page and calls the `callback` function once the value is ready (along with the relevant `largest-contentful-paint` performance entry used to determine the value). The reported value is a [`DOMHighResTimeStamp`](https://developer.mozilla.org/docs/Web/API/DOMHighResTimeStamp).
@@ -723,7 +719,10 @@ If the `reportAllChanges` [configuration option](#reportopts) is set to `true`,
 #### `onTTFB()`
 
 ```ts
-type onTTFB = (callback: TTFBReportCallback, opts?: ReportOpts) => void;
+function onTTFB(
+  callback: (metric: TTFBMetric) => void,
+  opts?: ReportOpts,
+): void;
 ```
 
 Calculates the [TTFB](https://web.dev/articles/ttfb) value for the current page and calls the `callback` function once the page has loaded, along with the relevant `navigation` performance entry used to determine the value. The reported value is a [`DOMHighResTimeStamp`](https://developer.mozilla.org/docs/Web/API/DOMHighResTimeStamp).
@@ -760,15 +759,17 @@ console.log(INPThresholds); // [ 200, 500 ]
 console.log(LCPThresholds); // [ 2500, 4000 ]
 ```
 
-_**Note:** It's typically not necessary (or recommended) to manually calculate metric value ratings using these thresholds. Use the [`Metric['rating']`](#metric) supplied by the [`ReportCallback`](#reportcallback) functions instead._
+_**Note:** It's typically not necessary (or recommended) to manually calculate metric value ratings using these thresholds. Use the [`Metric['rating']`](#metric) instead._
 
 ### Attribution:
 
 The following objects contain potentially-helpful debugging information that can be sent along with the metric values for the current page visit in order to help identify issues happening to real-users in the field.
 
+When using the attribution build, these objects are found as an `attribution` property on each metric.
+
 See the [attribution build](#attribution-build) section for details on how to use this feature.
 
-#### CLS `attribution`:
+#### [CLS `attribution`](/src/types/cls.ts#:~:text=interface%20CLSMetricWithAttribution)
 
 ```ts
 interface CLSAttribution {
@@ -809,7 +810,7 @@ interface CLSAttribution {
 }
 ```
 
-#### FCP `attribution`:
+#### [FCP `attribution`](/src/types/fcp.ts#:~:text=interface%20FCPMetricWithAttribution)
 
 ```ts
 interface FCPAttribution {
@@ -841,7 +842,7 @@ interface FCPAttribution {
 }
 ```
 
-#### FID `attribution`:
+#### [FID `attribution`](/src/types/fid.ts#:~:text=interface%20FIDMetricWithAttribution)
 
 ```ts
 interface FIDAttribution {
@@ -873,7 +874,7 @@ interface FIDAttribution {
 }
 ```
 
-#### INP `attribution`:
+#### [INP `attribution`](/src/types/inp.ts#:~:text=interface%20INPMetricWithAttribution)
 
 ```ts
 interface INPAttribution {
@@ -964,7 +965,7 @@ interface INPAttribution {
 }
 ```
 
-#### LCP `attribution`:
+#### [LCP `attribution`](/src/types/lcp.ts#:~:text=interface%20LCPMetricWithAttribution)
 
 ```ts
 interface LCPAttribution {
@@ -1019,7 +1020,7 @@ interface LCPAttribution {
 }
 ```
 
-#### TTFB `attribution`:
+#### [TTFB `attribution`](/src/types/ttfb.ts#:~:text=interface%20TTFBMetricWithAttribution)
 
 ```ts
 export interface TTFBAttribution {

From 6fa9082379a10656ec562f51f9910ca92e3b3c16 Mon Sep 17 00:00:00 2001
From: Brendan Kenny <bckenny@gmail.com>
Date: Thu, 2 May 2024 12:29:38 -0500
Subject: [PATCH 06/14] object.assign attributions

---
 src/attribution/onCLS.ts  | 5 ++---
 src/attribution/onFCP.ts  | 5 ++---
 src/attribution/onFID.ts  | 5 ++---
 src/attribution/onINP.ts  | 5 ++---
 src/attribution/onLCP.ts  | 5 ++---
 src/attribution/onTTFB.ts | 5 ++---
 6 files changed, 12 insertions(+), 18 deletions(-)

diff --git a/src/attribution/onCLS.ts b/src/attribution/onCLS.ts
index abd0d0cf..b4b80af5 100644
--- a/src/attribution/onCLS.ts
+++ b/src/attribution/onCLS.ts
@@ -53,9 +53,8 @@ const attributeCLS = (metric: CLSMetric): CLSMetricWithAttribution => {
     }
   }
 
-  // Cast to attribution metric so it can be populated.
-  const metricWithAttribution = metric as CLSMetricWithAttribution;
-  metricWithAttribution.attribution = attribution;
+  // Use Object.assign to set property to keep tsc happy.
+  const metricWithAttribution = Object.assign(metric, {attribution});
   return metricWithAttribution;
 };
 
diff --git a/src/attribution/onFCP.ts b/src/attribution/onFCP.ts
index 78790169..faa919f3 100644
--- a/src/attribution/onFCP.ts
+++ b/src/attribution/onFCP.ts
@@ -55,9 +55,8 @@ const attributeFCP = (metric: FCPMetric): FCPMetricWithAttribution => {
     }
   }
 
-  // Cast to attribution metric so it can be populated.
-  const metricWithAttribution = metric as FCPMetricWithAttribution;
-  metricWithAttribution.attribution = attribution;
+  // Use Object.assign to set property to keep tsc happy.
+  const metricWithAttribution = Object.assign(metric, {attribution});
   return metricWithAttribution;
 };
 
diff --git a/src/attribution/onFID.ts b/src/attribution/onFID.ts
index 9dcfd6dc..538adbb3 100644
--- a/src/attribution/onFID.ts
+++ b/src/attribution/onFID.ts
@@ -34,9 +34,8 @@ const attributeFID = (metric: FIDMetric): FIDMetricWithAttribution => {
     loadState: getLoadState(fidEntry.startTime),
   };
 
-  // Cast to attribution metric so it can be populated.
-  const metricWithAttribution = metric as FIDMetricWithAttribution;
-  metricWithAttribution.attribution = attribution;
+  // Use Object.assign to set property to keep tsc happy.
+  const metricWithAttribution = Object.assign(metric, {attribution});
   return metricWithAttribution;
 };
 
diff --git a/src/attribution/onINP.ts b/src/attribution/onINP.ts
index 91aba61d..338a50e8 100644
--- a/src/attribution/onINP.ts
+++ b/src/attribution/onINP.ts
@@ -240,9 +240,8 @@ const attributeINP = (metric: INPMetric): INPMetricWithAttribution => {
     loadState: getLoadState(firstEntry.startTime),
   };
 
-  // Cast to attribution metric so it can be populated.
-  const metricWithAttribution = metric as INPMetricWithAttribution;
-  metricWithAttribution.attribution = attribution;
+  // Use Object.assign to set property to keep tsc happy.
+  const metricWithAttribution = Object.assign(metric, {attribution});
   return metricWithAttribution;
 };
 
diff --git a/src/attribution/onLCP.ts b/src/attribution/onLCP.ts
index cdf56596..a7280675 100644
--- a/src/attribution/onLCP.ts
+++ b/src/attribution/onLCP.ts
@@ -85,9 +85,8 @@ const attributeLCP = (metric: LCPMetric): LCPMetricWithAttribution => {
     }
   }
 
-  // Cast to attribution metric so it can be populated.
-  const metricWithAttribution = metric as LCPMetricWithAttribution;
-  metricWithAttribution.attribution = attribution;
+  // Use Object.assign to set property to keep tsc happy.
+  const metricWithAttribution = Object.assign(metric, {attribution});
   return metricWithAttribution;
 };
 
diff --git a/src/attribution/onTTFB.ts b/src/attribution/onTTFB.ts
index 3c1529b8..5f4487ec 100644
--- a/src/attribution/onTTFB.ts
+++ b/src/attribution/onTTFB.ts
@@ -73,9 +73,8 @@ const attributeTTFB = (metric: TTFBMetric): TTFBMetricWithAttribution => {
     };
   }
 
-  // Cast to attribution metric so it can be populated.
-  const metricWithAttribution = metric as TTFBMetricWithAttribution;
-  metricWithAttribution.attribution = attribution;
+  // Use Object.assign to set property to keep tsc happy.
+  const metricWithAttribution = Object.assign(metric, {attribution});
   return metricWithAttribution;
 };
 

From da7bd49d2ff2d02738a8fb566f8a62aef3136975 Mon Sep 17 00:00:00 2001
From: Philip Walton <philip@philipwalton.com>
Date: Thu, 2 May 2024 21:06:20 -0700
Subject: [PATCH 07/14] Move isInvalidTimestamp into getNavigationEntry

---
 src/attribution/onFCP.ts      | 22 +++++++++-------------
 src/attribution/onLCP.ts      | 10 ++++------
 src/lib/getNavigationEntry.ts | 24 ++++++++++++++++++------
 src/onTTFB.ts                 | 16 +++++++---------
 4 files changed, 38 insertions(+), 34 deletions(-)

diff --git a/src/attribution/onFCP.ts b/src/attribution/onFCP.ts
index faa919f3..a17fdef2 100644
--- a/src/attribution/onFCP.ts
+++ b/src/attribution/onFCP.ts
@@ -17,7 +17,6 @@
 import {getBFCacheRestoreTime} from '../lib/bfcache.js';
 import {getLoadState} from '../lib/getLoadState.js';
 import {getNavigationEntry} from '../lib/getNavigationEntry.js';
-import {isInvalidTimestamp} from '../lib/isInvalidTimestamp.js';
 import {onFCP as unattributedOnFCP} from '../onFCP.js';
 import {
   FCPAttribution,
@@ -39,19 +38,16 @@ const attributeFCP = (metric: FCPMetric): FCPMetricWithAttribution => {
     const fcpEntry = metric.entries[metric.entries.length - 1];
 
     if (navigationEntry) {
-      const responseStart = navigationEntry.responseStart;
-      if (!isInvalidTimestamp(responseStart)) {
-        const activationStart = navigationEntry.activationStart || 0;
-        const ttfb = Math.max(0, responseStart - activationStart);
+      const activationStart = navigationEntry.activationStart || 0;
+      const ttfb = Math.max(0, navigationEntry.responseStart - activationStart);
 
-        attribution = {
-          timeToFirstByte: ttfb,
-          firstByteToFCP: metric.value - ttfb,
-          loadState: getLoadState(metric.entries[0].startTime),
-          navigationEntry,
-          fcpEntry,
-        };
-      }
+      attribution = {
+        timeToFirstByte: ttfb,
+        firstByteToFCP: metric.value - ttfb,
+        loadState: getLoadState(metric.entries[0].startTime),
+        navigationEntry,
+        fcpEntry,
+      };
     }
   }
 
diff --git a/src/attribution/onLCP.ts b/src/attribution/onLCP.ts
index a7280675..db732e0f 100644
--- a/src/attribution/onLCP.ts
+++ b/src/attribution/onLCP.ts
@@ -16,7 +16,6 @@
 
 import {getNavigationEntry} from '../lib/getNavigationEntry.js';
 import {getSelector} from '../lib/getSelector.js';
-import {isInvalidTimestamp} from '../lib/isInvalidTimestamp.js';
 import {onLCP as unattributedOnLCP} from '../onLCP.js';
 import {
   LCPAttribution,
@@ -34,10 +33,9 @@ const attributeLCP = (metric: LCPMetric): LCPMetricWithAttribution => {
     elementRenderDelay: metric.value,
   };
 
-  const navigationEntry = getNavigationEntry();
-  if (metric.entries.length && navigationEntry) {
-    const responseStart = navigationEntry.responseStart;
-    if (!isInvalidTimestamp(responseStart)) {
+  if (metric.entries.length) {
+    const navigationEntry = getNavigationEntry();
+    if (navigationEntry) {
       const activationStart = navigationEntry.activationStart || 0;
       const lcpEntry = metric.entries[metric.entries.length - 1];
       const lcpResourceEntry =
@@ -46,7 +44,7 @@ const attributeLCP = (metric: LCPMetric): LCPMetricWithAttribution => {
           .getEntriesByType('resource')
           .filter((e) => e.name === lcpEntry.url)[0];
 
-      const ttfb = Math.max(0, responseStart - activationStart);
+      const ttfb = Math.max(0, navigationEntry.responseStart - activationStart);
 
       const lcpRequestStart = Math.max(
         ttfb,
diff --git a/src/lib/getNavigationEntry.ts b/src/lib/getNavigationEntry.ts
index e575c584..19d18cf5 100644
--- a/src/lib/getNavigationEntry.ts
+++ b/src/lib/getNavigationEntry.ts
@@ -14,12 +14,24 @@
  * limitations under the License.
  */
 
-export const getNavigationEntry = ():
-  | PerformanceNavigationTiming
-  | undefined => {
-  return (
+export const getNavigationEntry = (): PerformanceNavigationTiming | void => {
+  const navigationEntry =
     self.performance &&
     performance.getEntriesByType &&
-    performance.getEntriesByType('navigation')[0]
-  );
+    performance.getEntriesByType('navigation')[0];
+
+  // Check to ensure the `responseStart` property is present and valid.
+  // In some cases no value is reported by the browser (for
+  // privacy/security reasons), and in other cases (bugs) the value is
+  // negative or is larger than the current page time. Ignore these cases:
+  // https://github.com/GoogleChrome/web-vitals/issues/137
+  // https://github.com/GoogleChrome/web-vitals/issues/162
+  // https://github.com/GoogleChrome/web-vitals/issues/275
+  if (
+    navigationEntry &&
+    navigationEntry.responseStart > 0 &&
+    navigationEntry.responseStart < performance.now()
+  ) {
+    return navigationEntry;
+  }
 };
diff --git a/src/onTTFB.ts b/src/onTTFB.ts
index a9c19d98..8167a568 100644
--- a/src/onTTFB.ts
+++ b/src/onTTFB.ts
@@ -16,7 +16,6 @@
 
 import {bindReporter} from './lib/bindReporter.js';
 import {initMetric} from './lib/initMetric.js';
-import {isInvalidTimestamp} from './lib/isInvalidTimestamp.js';
 import {onBFCacheRestore} from './lib/bfcache.js';
 import {getNavigationEntry} from './lib/getNavigationEntry.js';
 import {MetricRatingThresholds, ReportOpts, TTFBMetric} from './types.js';
@@ -72,20 +71,19 @@ export const onTTFB = (
   );
 
   whenReady(() => {
-    const navEntry = getNavigationEntry();
-
-    if (navEntry) {
-      const responseStart = navEntry.responseStart;
-
-      if (isInvalidTimestamp(responseStart)) return;
+    const navigationEntry = getNavigationEntry();
 
+    if (navigationEntry) {
       // The activationStart reference is used because TTFB should be
       // relative to page activation rather than navigation start if the
       // page was prerendered. But in cases where `activationStart` occurs
       // after the first byte is received, this time should be clamped at 0.
-      metric.value = Math.max(responseStart - getActivationStart(), 0);
+      metric.value = Math.max(
+        navigationEntry.responseStart - getActivationStart(),
+        0,
+      );
 
-      metric.entries = [navEntry];
+      metric.entries = [navigationEntry];
       report(true);
 
       // Only report TTFB after bfcache restores if a `navigation` entry

From 06d9217db4dfd042322609235d591f5481e88cf6 Mon Sep 17 00:00:00 2001
From: Philip Walton <philip@philipwalton.com>
Date: Thu, 2 May 2024 21:17:32 -0700
Subject: [PATCH 08/14] Explicitly type attribution return values

---
 src/attribution/onCLS.ts  | 5 ++++-
 src/attribution/onFCP.ts  | 5 ++++-
 src/attribution/onFID.ts  | 5 ++++-
 src/attribution/onINP.ts  | 5 ++++-
 src/attribution/onLCP.ts  | 5 ++++-
 src/attribution/onTTFB.ts | 5 ++++-
 6 files changed, 24 insertions(+), 6 deletions(-)

diff --git a/src/attribution/onCLS.ts b/src/attribution/onCLS.ts
index b4b80af5..52e2bee4 100644
--- a/src/attribution/onCLS.ts
+++ b/src/attribution/onCLS.ts
@@ -54,7 +54,10 @@ const attributeCLS = (metric: CLSMetric): CLSMetricWithAttribution => {
   }
 
   // Use Object.assign to set property to keep tsc happy.
-  const metricWithAttribution = Object.assign(metric, {attribution});
+  const metricWithAttribution: CLSMetricWithAttribution = Object.assign(
+    metric,
+    {attribution},
+  );
   return metricWithAttribution;
 };
 
diff --git a/src/attribution/onFCP.ts b/src/attribution/onFCP.ts
index a17fdef2..079bf91a 100644
--- a/src/attribution/onFCP.ts
+++ b/src/attribution/onFCP.ts
@@ -52,7 +52,10 @@ const attributeFCP = (metric: FCPMetric): FCPMetricWithAttribution => {
   }
 
   // Use Object.assign to set property to keep tsc happy.
-  const metricWithAttribution = Object.assign(metric, {attribution});
+  const metricWithAttribution: FCPMetricWithAttribution = Object.assign(
+    metric,
+    {attribution},
+  );
   return metricWithAttribution;
 };
 
diff --git a/src/attribution/onFID.ts b/src/attribution/onFID.ts
index 538adbb3..ed561429 100644
--- a/src/attribution/onFID.ts
+++ b/src/attribution/onFID.ts
@@ -35,7 +35,10 @@ const attributeFID = (metric: FIDMetric): FIDMetricWithAttribution => {
   };
 
   // Use Object.assign to set property to keep tsc happy.
-  const metricWithAttribution = Object.assign(metric, {attribution});
+  const metricWithAttribution: FIDMetricWithAttribution = Object.assign(
+    metric,
+    {attribution},
+  );
   return metricWithAttribution;
 };
 
diff --git a/src/attribution/onINP.ts b/src/attribution/onINP.ts
index 338a50e8..3c103fe2 100644
--- a/src/attribution/onINP.ts
+++ b/src/attribution/onINP.ts
@@ -241,7 +241,10 @@ const attributeINP = (metric: INPMetric): INPMetricWithAttribution => {
   };
 
   // Use Object.assign to set property to keep tsc happy.
-  const metricWithAttribution = Object.assign(metric, {attribution});
+  const metricWithAttribution: INPMetricWithAttribution = Object.assign(
+    metric,
+    {attribution},
+  );
   return metricWithAttribution;
 };
 
diff --git a/src/attribution/onLCP.ts b/src/attribution/onLCP.ts
index db732e0f..285f319a 100644
--- a/src/attribution/onLCP.ts
+++ b/src/attribution/onLCP.ts
@@ -84,7 +84,10 @@ const attributeLCP = (metric: LCPMetric): LCPMetricWithAttribution => {
   }
 
   // Use Object.assign to set property to keep tsc happy.
-  const metricWithAttribution = Object.assign(metric, {attribution});
+  const metricWithAttribution: LCPMetricWithAttribution = Object.assign(
+    metric,
+    {attribution},
+  );
   return metricWithAttribution;
 };
 
diff --git a/src/attribution/onTTFB.ts b/src/attribution/onTTFB.ts
index 5f4487ec..1cfd74bc 100644
--- a/src/attribution/onTTFB.ts
+++ b/src/attribution/onTTFB.ts
@@ -74,7 +74,10 @@ const attributeTTFB = (metric: TTFBMetric): TTFBMetricWithAttribution => {
   }
 
   // Use Object.assign to set property to keep tsc happy.
-  const metricWithAttribution = Object.assign(metric, {attribution});
+  const metricWithAttribution: TTFBMetricWithAttribution = Object.assign(
+    metric,
+    {attribution},
+  );
   return metricWithAttribution;
 };
 

From 1844113461fd6a6cfaace2b2a4f9ddf0ed2f16c4 Mon Sep 17 00:00:00 2001
From: Philip Walton <philip@philipwalton.com>
Date: Thu, 2 May 2024 21:22:42 -0700
Subject: [PATCH 09/14] Remove missed file

---
 src/lib/isInvalidTimestamp.ts | 25 -------------------------
 1 file changed, 25 deletions(-)
 delete mode 100644 src/lib/isInvalidTimestamp.ts

diff --git a/src/lib/isInvalidTimestamp.ts b/src/lib/isInvalidTimestamp.ts
deleted file mode 100644
index 4311cf71..00000000
--- a/src/lib/isInvalidTimestamp.ts
+++ /dev/null
@@ -1,25 +0,0 @@
-/*
- * Copyright 2024 Google LLC
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     https://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-export const isInvalidTimestamp = (timestamp: DOMHighResTimeStamp) => {
-  // In some cases no value is reported by the browser (for
-  // privacy/security reasons), and in other cases (bugs) the value is
-  // negative or is larger than the current page time. Ignore these cases:
-  // https://github.com/GoogleChrome/web-vitals/issues/137
-  // https://github.com/GoogleChrome/web-vitals/issues/162
-  // https://github.com/GoogleChrome/web-vitals/issues/275
-  return timestamp <= 0 || timestamp > performance.now();
-};

From f3e826147d90de15d32826b1eb09a8d54f660134 Mon Sep 17 00:00:00 2001
From: Philip Walton <philip@philipwalton.com>
Date: Thu, 2 May 2024 21:51:40 -0700
Subject: [PATCH 10/14] Update README

---
 README.md | 126 ++++++++++++++++++++++++++++++------------------------
 1 file changed, 69 insertions(+), 57 deletions(-)

diff --git a/README.md b/README.md
index 646246df..b75cbc20 100644
--- a/README.md
+++ b/README.md
@@ -490,7 +490,75 @@ For guidance on how to collect and use real-user data to debug performance issue
 
 ### Types
 
-#### Metrics
+#### `Metric`
+
+All metrics types inherit from the following base interface:
+
+```ts
+interface Metric {
+  /**
+   * The name of the metric (in acronym form).
+   */
+  name: 'CLS' | 'FCP' | 'FID' | 'INP' | 'LCP' | 'TTFB';
+
+  /**
+   * The current value of the metric.
+   */
+  value: number;
+
+  /**
+   * The rating as to whether the metric value is within the "good",
+   * "needs improvement", or "poor" thresholds of the metric.
+   */
+  rating: 'good' | 'needs-improvement' | 'poor';
+
+  /**
+   * The delta between the current value and the last-reported value.
+   * On the first report, `delta` and `value` will always be the same.
+   */
+  delta: number;
+
+  /**
+   * A unique ID representing this particular metric instance. This ID can
+   * be used by an analytics tool to dedupe multiple values sent for the same
+   * metric instance, or to group multiple deltas together and calculate a
+   * total. It can also be used to differentiate multiple different metric
+   * instances sent from the same page, which can happen if the page is
+   * restored from the back/forward cache (in that case new metrics object
+   * get created).
+   */
+  id: string;
+
+  /**
+   * Any performance entries relevant to the metric value calculation.
+   * The array may also be empty if the metric value was not based on any
+   * entries (e.g. a CLS value of 0 given no layout shifts).
+   */
+  entries: PerformanceEntry[];
+
+  /**
+   * The type of navigation.
+   *
+   * This will be the value returned by the Navigation Timing API (or
+   * `undefined` if the browser doesn't support that API), with the following
+   * exceptions:
+   * - 'back-forward-cache': for pages that are restored from the bfcache.
+   * - 'back_forward' is renamed to 'back-forward' for consistency.
+   * - 'prerender': for pages that were prerendered.
+   * - 'restore': for pages that were discarded by the browser and then
+   * restored by the user.
+   */
+  navigationType:
+    | 'navigate'
+    | 'reload'
+    | 'back-forward'
+    | 'back-forward-cache'
+    | 'prerender'
+    | 'restore';
+}
+```
+
+Metric-specific subclasses:
 
 ##### [`CLSMetric`](/src/types/cls.ts#:~:text=interface%20CLSMetric)
 
@@ -546,62 +614,6 @@ interface TTFBMetric extends Metric {
 }
 ```
 
-##### `Metric`
-
-All metrics share the following properties:
-
-```ts
-interface Metric {
-  /**
-   * The current value of the metric.
-   */
-  value: number;
-
-  /**
-   * The rating as to whether the metric value is within the "good",
-   * "needs improvement", or "poor" thresholds of the metric.
-   */
-  rating: 'good' | 'needs-improvement' | 'poor';
-
-  /**
-   * The delta between the current value and the last-reported value.
-   * On the first report, `delta` and `value` will always be the same.
-   */
-  delta: number;
-
-  /**
-   * A unique ID representing this particular metric instance. This ID can
-   * be used by an analytics tool to dedupe multiple values sent for the same
-   * metric instance, or to group multiple deltas together and calculate a
-   * total. It can also be used to differentiate multiple different metric
-   * instances sent from the same page, which can happen if the page is
-   * restored from the back/forward cache (in that case new metrics object
-   * get created).
-   */
-  id: string;
-
-  /**
-   * The type of navigation.
-   *
-   * This will be the value returned by the Navigation Timing API (or
-   * `undefined` if the browser doesn't support that API), with the following
-   * exceptions:
-   * - 'back-forward-cache': for pages that are restored from the bfcache.
-   * - 'back_forward' is renamed to 'back-forward' for consistency.
-   * - 'prerender': for pages that were prerendered.
-   * - 'restore': for pages that were discarded by the browser and then
-   * restored by the user.
-   */
-  navigationType:
-    | 'navigate'
-    | 'reload'
-    | 'back-forward'
-    | 'back-forward-cache'
-    | 'prerender'
-    | 'restore';
-}
-```
-
 #### `MetricRatingThresholds`
 
 The thresholds of metric's "good", "needs improvement", and "poor" ratings.

From 1d15a33251ef8c270d6c123bb015e4fc33d355be Mon Sep 17 00:00:00 2001
From: Philip Walton <philipwalton@users.noreply.github.com>
Date: Fri, 3 May 2024 06:51:38 -0700
Subject: [PATCH 11/14] Apply suggestions from code review

Co-authored-by: Barry Pollard <barrypollard@google.com>
---
 README.md | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/README.md b/README.md
index b75cbc20..35c58b04 100644
--- a/README.md
+++ b/README.md
@@ -490,7 +490,7 @@ For guidance on how to collect and use real-user data to debug performance issue
 
 ### Types
 
-#### `Metric`
+#### [`Metric`](/src/types/base.ts#:~:text=interface%20Metric)
 
 All metrics types inherit from the following base interface:
 
@@ -781,7 +781,7 @@ When using the attribution build, these objects are found as an `attribution` pr
 
 See the [attribution build](#attribution-build) section for details on how to use this feature.
 
-#### [CLS `attribution`](/src/types/cls.ts#:~:text=interface%20CLSMetricWithAttribution)
+#### [CLS `attribution`](/src/types/cls.ts#:~:text=interface%20CLSAttribution)
 
 ```ts
 interface CLSAttribution {
@@ -822,7 +822,7 @@ interface CLSAttribution {
 }
 ```
 
-#### [FCP `attribution`](/src/types/fcp.ts#:~:text=interface%20FCPMetricWithAttribution)
+#### [FCP `attribution`](/src/types/fcp.ts#:~:text=interface%20FCPAttribution)
 
 ```ts
 interface FCPAttribution {
@@ -854,7 +854,7 @@ interface FCPAttribution {
 }
 ```
 
-#### [FID `attribution`](/src/types/fid.ts#:~:text=interface%20FIDMetricWithAttribution)
+#### [FID `attribution`](/src/types/fid.ts#:~:text=interface%20FIDAttribution)
 
 ```ts
 interface FIDAttribution {
@@ -886,7 +886,7 @@ interface FIDAttribution {
 }
 ```
 
-#### [INP `attribution`](/src/types/inp.ts#:~:text=interface%20INPMetricWithAttribution)
+#### [INP `attribution`](/src/types/inp.ts#:~:text=interface%20INPAttribution)
 
 ```ts
 interface INPAttribution {
@@ -977,7 +977,7 @@ interface INPAttribution {
 }
 ```
 
-#### [LCP `attribution`](/src/types/lcp.ts#:~:text=interface%20LCPMetricWithAttribution)
+#### [LCP `attribution`](/src/types/lcp.ts#:~:text=interface%20LCPAttribution)
 
 ```ts
 interface LCPAttribution {
@@ -1032,7 +1032,7 @@ interface LCPAttribution {
 }
 ```
 
-#### [TTFB `attribution`](/src/types/ttfb.ts#:~:text=interface%20TTFBMetricWithAttribution)
+#### [TTFB `attribution`](/src/types/ttfb.ts#:~:text=interface%20TTFBAttribution)
 
 ```ts
 export interface TTFBAttribution {

From f22e94de5b2baa7ed937de434406559ea840b41b Mon Sep 17 00:00:00 2001
From: Philip Walton <philip@philipwalton.com>
Date: Fri, 3 May 2024 07:30:39 -0700
Subject: [PATCH 12/14] Remove src files links in README

---
 README.md | 28 ++++++++++++++--------------
 1 file changed, 14 insertions(+), 14 deletions(-)

diff --git a/README.md b/README.md
index 35c58b04..d733f2a7 100644
--- a/README.md
+++ b/README.md
@@ -488,9 +488,9 @@ For guidance on how to collect and use real-user data to debug performance issue
 
 ## API
 
-### Types
+### Types:
 
-#### [`Metric`](/src/types/base.ts#:~:text=interface%20Metric)
+#### `Metric`
 
 All metrics types inherit from the following base interface:
 
@@ -560,7 +560,7 @@ interface Metric {
 
 Metric-specific subclasses:
 
-##### [`CLSMetric`](/src/types/cls.ts#:~:text=interface%20CLSMetric)
+##### `CLSMetric`
 
 ```ts
 interface CLSMetric extends Metric {
@@ -569,7 +569,7 @@ interface CLSMetric extends Metric {
 }
 ```
 
-##### [`FCPMetric`](/src/types/fcp.ts#:~:text=interface%20FCPMetric)
+##### `FCPMetric`
 
 ```ts
 interface FCPMetric extends Metric {
@@ -578,7 +578,7 @@ interface FCPMetric extends Metric {
 }
 ```
 
-##### [`FIDMetric`](/src/types/fid.ts#:~:text=interface%20FIDMetric)
+##### `FIDMetric`
 
 ```ts
 interface FIDMetric extends Metric {
@@ -587,7 +587,7 @@ interface FIDMetric extends Metric {
 }
 ```
 
-##### [`INPMetric`](/src/types/inp.ts#:~:text=interface%20INPMetric)
+##### `INPMetric`
 
 ```ts
 interface INPMetric extends Metric {
@@ -596,7 +596,7 @@ interface INPMetric extends Metric {
 }
 ```
 
-##### [`LCPMetric`](/src/types/lcp.ts#:~:text=interface%20LCPMetric)
+##### `LCPMetric`
 
 ```ts
 interface LCPMetric extends Metric {
@@ -605,7 +605,7 @@ interface LCPMetric extends Metric {
 }
 ```
 
-##### [`TTFBMetric`](/src/types/ttfb.ts#:~:text=interface%20TTFBMetric)
+##### `TTFBMetric`
 
 ```ts
 interface TTFBMetric extends Metric {
@@ -781,7 +781,7 @@ When using the attribution build, these objects are found as an `attribution` pr
 
 See the [attribution build](#attribution-build) section for details on how to use this feature.
 
-#### [CLS `attribution`](/src/types/cls.ts#:~:text=interface%20CLSAttribution)
+#### `CLSAttribution`
 
 ```ts
 interface CLSAttribution {
@@ -822,7 +822,7 @@ interface CLSAttribution {
 }
 ```
 
-#### [FCP `attribution`](/src/types/fcp.ts#:~:text=interface%20FCPAttribution)
+#### `FCPAttribution`
 
 ```ts
 interface FCPAttribution {
@@ -854,7 +854,7 @@ interface FCPAttribution {
 }
 ```
 
-#### [FID `attribution`](/src/types/fid.ts#:~:text=interface%20FIDAttribution)
+#### `FIDAttribution`
 
 ```ts
 interface FIDAttribution {
@@ -886,7 +886,7 @@ interface FIDAttribution {
 }
 ```
 
-#### [INP `attribution`](/src/types/inp.ts#:~:text=interface%20INPAttribution)
+#### `INPAttribution`
 
 ```ts
 interface INPAttribution {
@@ -977,7 +977,7 @@ interface INPAttribution {
 }
 ```
 
-#### [LCP `attribution`](/src/types/lcp.ts#:~:text=interface%20LCPAttribution)
+#### `LCPAttribution`
 
 ```ts
 interface LCPAttribution {
@@ -1032,7 +1032,7 @@ interface LCPAttribution {
 }
 ```
 
-#### [TTFB `attribution`](/src/types/ttfb.ts#:~:text=interface%20TTFBAttribution)
+#### `TTFBAttribution`
 
 ```ts
 export interface TTFBAttribution {

From 2c7f648dc59ac8233aeac4818fe988aa48be9f27 Mon Sep 17 00:00:00 2001
From: Philip Walton <philip@philipwalton.com>
Date: Fri, 3 May 2024 09:20:31 -0700
Subject: [PATCH 13/14] Fix README error

---
 README.md | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/README.md b/README.md
index 8a75d54c..8b839d11 100644
--- a/README.md
+++ b/README.md
@@ -100,7 +100,7 @@ To load the "attribution" build, change any `import` statements that reference `
 + import {onLCP, onINP, onCLS} from 'web-vitals/attribution';
 ```
 
-Usage for each of the imported function is identical to the standard build, but when importing from the attribution build, the [metrics](#metrics) objects will contain an additional [`attribution`](#attribution) property.
+Usage for each of the imported function is identical to the standard build, but when importing from the attribution build, the [metric](#metric) objects will contain an additional [`attribution`](#attribution) property.
 
 See [Send attribution data](#send-attribution-data) for usage examples, and the [`attribution` reference](#attribution) for details on what values are added for each metric.
 
@@ -580,6 +580,8 @@ interface FCPMetric extends Metric {
 
 ##### `FIDMetric`
 
+_This interface is deprecated and will be removed in next major release_
+
 ```ts
 interface FIDMetric extends Metric {
   name: 'FID';
@@ -694,7 +696,7 @@ Calculates the [FCP](https://web.dev/articles/fcp) value for the current page an
 
 #### `onFID()`
 
-_Deprecated and will be removed in next major release_
+_This function is deprecated and will be removed in next major release_
 
 ```ts
 function onFID(callback: (metric: FIDMetric) => void, opts?: ReportOpts): void;

From c80d9f3a7e6db031f5b088385174a60a7d1f5858 Mon Sep 17 00:00:00 2001
From: Philip Walton <philip@philipwalton.com>
Date: Fri, 3 May 2024 09:27:37 -0700
Subject: [PATCH 14/14] Add one more note to README

---
 README.md | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/README.md b/README.md
index 8b839d11..2119358c 100644
--- a/README.md
+++ b/README.md
@@ -858,6 +858,8 @@ interface FCPAttribution {
 
 #### `FIDAttribution`
 
+_This interface is deprecated and will be removed in next major release_
+
 ```ts
 interface FIDAttribution {
   /**