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。
The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.
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 -
从
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
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
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
|
Legend
- Full support
- Full support
- No support
- No support
- User must explicitly enable this feature.
- User must explicitly enable this feature.