Array.prototype.includes()

 

includes() 方法用来判断一个数组是否包含一个指定的值,根据情况,如果包含则返回 true,否则返回false。

语法

arr.includes(valueToFind[fromIndex])

参数

valueToFind

需要查找的元素值。

Note:  使用 includes()比较字符串和字符时是区分大小写。

fromIndex 可选
fromIndex 索引处开始查找 valueToFind。如果为负值,则按升序从 array.length + fromIndex 的索引开始搜 (即使从末尾开始往前跳 fromIndex 的绝对值个索引,然后往后搜寻)。默认为 0。

返回值

A Boolean which is true if the value valueToFind is found within the array (or the part of the array indicated by the index fromIndex, if specified). Values of zero are all considered to be equal regardless of sign (that is, -0 is considered to be equal to both 0 and +0), but false is not considered to be the same as 0.

返回一个布尔值 Boolean ,如果在数组中找到了(如果传入了 fromIndex ,表示在 fromIndex 指定的索引范围中找到了)则返回 true 。

Note: Technically speaking, includes() uses the sameValueZero algorithm to determine whether the given element is found.

示例

[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 大于等于数组长度

如果 fromIndex 大于等于数组的长度,则会返回 false,且该数组不会被搜索。

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

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

计算出的索引小于 0

如果 fromIndex 为负值,计算出的索引将作为开始搜索searchElement的位置。如果计算出的索引小于 0,则整个数组都会被搜索。

// 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

作为通用方法的 includes()

includes() 方法有意设计为通用方法。它不要求this值是数组对象,所以它可以被用于其他类型的对象 (比如类数组对象)。下面的例子展示了 在函数的 arguments 对象上调用的 includes() 方法。

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

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

如果你需要支持那些不支持Object.defineProperty的废弃JavaScript 引擎,你最好不要 polyfill Array.prototype 方法,因为你不能使它们不可枚举。

规范

规范 状态 备注
ECMAScript 2016 (ECMA-262)
Array.prototype.includes
Standard Initial definition.
ECMAScript Latest Draft (ECMA-262)
Array.prototype.includes
Draft

浏览器兼容性

Update compatibility data on GitHub
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Chrome Edge Firefox Internet Explorer Opera Safari Android webview Chrome for Android Firefox for Android Opera for Android Safari on iOS Samsung Internet Node.js
includes Chrome Full support 47 Edge Full support 14 Firefox Full support 43 IE No support No Opera Full support 34 Safari Full support 9 WebView Android Full support Yes Chrome Android Full support 47 Firefox Android Full support 43 Opera Android Full support 34 Safari iOS Full support 9 Samsung Internet Android Full support Yes nodejs 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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参见