Array.prototype.includes()

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De includes() methode controleert of de opgegeven waarde reeds aanwezig is of niet, en geeft vervolgens true terug als dit klopt, anders false.

var a = [1, 2, 3];
a.includes(2); // true 
a.includes(4); // false

Syntax

arr.includes(searchElement)
arr.includes(searchElement, fromIndex)

Parameters

searchElement
Het element om te zoeken.
fromIndex Optional
De positie binnen de array waar begonnen wordt met het zoeken naar searchElement. A negative value searches from the index of array.length + fromIndex by asc. Defaults to 0.

Return value

Een Boolean.

Examples

[1, 2, 3].includes(2);     // true
[1, 2, 3].includes(4);     // false
[1, 2, 3].includes(3, 3);  // false
[1, 2, 3].includes(3, -1); // true
[1, 2, NaN].includes(NaN); // true

fromIndex is greater than or equal to the array length

If fromIndex is greater than or equal to the length of the array, false is returned. The array will not be searched.

var arr = ['a', 'b', 'c'];

arr.includes('c', 3);   //false
arr.includes('c', 100); // false

Computed index is less than 0

If fromIndex is negative, the computed index is calculated to be used as a position in the array at which to begin searching for searchElement. If the computed index is less than 0, the entire array will be searched.

// array length is 3
// fromIndex is -100
// computed index is 3 + (-100) = -97

var arr = ['a', 'b', 'c'];

arr.includes('a', -100); // true
arr.includes('b', -100); // true
arr.includes('c', -100); // true

includes() used as a generic method

includes() method is intentionally generic. It does not require this value to be an Array object, so it can be applied to other kinds of objects (e.g. array-like objects). The example below illustrates includes() method called on the function's arguments object.

(function() {
  console.log([].includes.call(arguments, 'a')); // true
  console.log([].includes.call(arguments, 'd')); // false
})('a','b','c');

Polyfill

// https://tc39.github.io/ecma262/#sec-array.prototype.includes
if (!Array.prototype.includes) {
  Object.defineProperty(Array.prototype, 'includes', {
    value: function(searchElement, fromIndex) {

      // 1. Let O be ? ToObject(this value).
      if (this == null) {
        throw new TypeError('"this" is null or not defined');
      }

      var o = Object(this);

      // 2. Let len be ? ToLength(? Get(O, "length")).
      var len = o.length >>> 0;

      // 3. If len is 0, return false.
      if (len === 0) {
        return false;
      }

      // 4. Let n be ? ToInteger(fromIndex).
      //    (If fromIndex is undefined, this step produces the value 0.)
      var n = fromIndex | 0;

      // 5. If n ≥ 0, then
      //  a. Let k be n.
      // 6. Else n < 0,
      //  a. Let k be len + n.
      //  b. If k < 0, let k be 0.
      var k = Math.max(n >= 0 ? n : len - Math.abs(n), 0);

      // 7. Repeat, while k < len
      while (k < len) {
        // a. Let elementK be the result of ? Get(O, ! ToString(k)).
        // b. If SameValueZero(searchElement, elementK) is true, return true.
        // c. Increase k by 1.
        // NOTE: === provides the correct "SameValueZero" comparison needed here.
        if (o[k] === searchElement) {
          return true;
        }
        k++;
      }

      // 8. Return false
      return false;
    }
  });
}

If you need to support truly obsolete JavaScript engines that don't support Object.defineProperty, it's best not to polyfill Array.prototype methods at all, as you can't make them non-enumerable.

Specifications

Specification Status Comment
ECMAScript 2016 (ECMA-262)
The definition of 'Array.prototype.includes' in that specification.
Standard Initial definition.
ECMAScript 2017 Draft (ECMA-262)
The definition of 'Array.prototype.includes' in that specification.
Draft  

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Edge Opera Safari
Basic support

47

43 (43) No support 14 34 9
Feature Android Android Webview Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile Chrome for Android
Basic support No support

47

43.0 (43) No support 34 9

47

See also

Documentlabels en -medewerkers

 Aan deze pagina hebben bijgedragen: SebastiaanNijland, juleskreutzer
 Laatst bijgewerkt door: SebastiaanNijland,