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includes() 메서드는 배열에 특정 요소가 포함되어 있는지 여부를 확인하여 적절하게 true 또는 false를 반환합니다.

구문

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

매개변수

searchElement
검색 할 요소입니다.
fromIndex Optional
이 배열에서 searchElement 검색을 시작할 위치입니다. 음의 값은 array.length + fromIndex의 인덱스를 asc로 검색합니다. 기본값은 0입니다.

반환 값

A Boolean.

예제

[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 or equal than -1 * array.length, 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
arr.includes('a', -2); // false

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');

폴리필

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

      if (this == null) {
        throw new TypeError('"this" is null or not defined');
      }

      // 1. Let O be ? ToObject(this value).
      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);

      function sameValueZero(x, y) {
        return x === y || (typeof x === 'number' && typeof y === 'number' && isNaN(x) && isNaN(y));
      }

      // 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.
        if (sameValueZero(o[k], searchElement)) {
          return true;
        }
        // c. Increase k by 1. 
        k++;
      }

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

명세

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

브라우저 호환성

Update compatibility data on GitHub
DesktopMobileServer
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidSafari on iOSSamsung InternetNode.js
Basic supportChrome Full support 47Edge Full support 14Firefox Full support 43IE No support NoOpera Full support 34Safari Full support 9WebView Android Full support YesChrome Android Full support YesEdge Mobile Full support 14Firefox Android Full support 43Opera Android Full support 34Safari iOS Full support 9Samsung Internet Android Full support Yesnodejs Full support 6.0.0
Full support 6.0.0
Full support 5.0.0
Disabled
Disabled From version 5.0.0: this feature is behind the --harmony runtime flag.

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Full support
No support  
No support
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User must explicitly enable this feature.

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