isExact feature along with its tests and readme changes

README.md

@@ -139,7 +139,7 @@ Validator                               | Description
 **isJSON(str [, options])**             | check if the string is valid JSON (note: uses JSON.parse).<br/><br/>`options` is an object which defaults to `{ allow_primitives: false }`. If `allow_primitives` is true, the primitives 'true', 'false' and 'null' are accepted as valid JSON values.
 **isJWT(str)**                         | check if the string is valid JWT token.
 **isLatLong(str [, options])**                      | check if the string is a valid latitude-longitude coordinate in the format `lat,long` or `lat, long`.<br/><br/>`options` is an object that defaults to `{ checkDMS: false }`. Pass `checkDMS` as `true` to validate DMS(degrees, minutes, and seconds) latitude-longitude format.
-**isLength(str [, options])**              | check if the string's length falls in a range.<br/><br/>`options` is an object which defaults to `{min:0, max: undefined}`. Note: this function takes into account surrogate pairs.
+**isLength(str [, options])**              | check if the string's length falls in a range and can receive an extra argument that is an array of numbers used to ask the string's length is exact of one of these elements.<br/><br/>`options` is an object which defaults to `{min:0, max: undefined, exact:[]}`. Note: this function takes into account surrogate pairs.
 **isLicensePlate(str [, locale])**     | check if string matches the format of a country's license plate.<br/><br/>(locale is one of `['cs-CZ', 'de-DE', 'de-LI', 'fi-FI', 'pt-BR', 'pt-PT', 'sq-AL', 'sv-SE']` or `any`)
 **isLocale(str)**                       | check if the string is a locale
 **isLowercase(str)**                    | check if the string is lowercase.

src/lib/isLength.js

@@ -1,18 +1,32 @@
-import assertString from './util/assertString';
+import assertString from './assertString';
 
 /* eslint-disable prefer-rest-params */
 export default function isLength(str, options) {
   assertString(str);
   let min;
   let max;
+  let exact;
+  let match = false;
   if (typeof (options) === 'object') {
     min = options.min || 0;
     max = options.max;
+    exact = options.exact
   } else { // backwards compatibility: isLength(str, min [, max])
     min = arguments[1] || 0;
     max = arguments[2];
+    exact = arguments[3];
+
   }
   const surrogatePairs = str.match(/[\uD800-\uDBFF][\uDC00-\uDFFF]/g) || [];
   const len = str.length - surrogatePairs.length;
-  return len >= min && (typeof max === 'undefined' || len <= max);
-}
+  if (exact && (len >= min && (typeof max === 'undefined' || len <= max))) {
+    exact.forEach(element => {
+      if(len === element){
+        match = true;
+      }
+    })
+  } else {
+    return len >= min && (typeof max === 'undefined' || len <= max);
+  }
+  return match;
+}

test/validators.js

@@ -4578,8 +4578,20 @@ describe('Validators', () => {
     });
     test({
       validator: 'isLength',
-      args: [{ max: 0 }],
-      valid: [''],
+      args: [{ min: 2, max: 8, exact: [4, 5, 6] }],
+      valid: ['abcd', 'abcde', 'abcdef'],
+      invalid: ['ab', 'abc'],
+    });
+    test({
+      validator: 'isLength',
+      args: [{ min: 5, max: 8, exact: [3, 4, 8] }],
+      valid: ['abcdefgh'],
+      invalid: ['abc', 'abcd'],
+    });
+    test({
+      validator: 'isLength',
+      args: [{ min: 3, max: 4, exact: [3, 4] }],
+      valid: ['abc', 'abcd', 'abcde'],
       invalid: ['a', 'ab'],
     });
     test({