path: root/files/zh-cn/web/javascript/reference/global_objects/array/from/index.html

---
title: Array.from()
slug: Web/JavaScript/Reference/Global_Objects/Array/from
tags:
  - Array
  - ECMAScript 2015
  - JavaScript
  - Reference
  - arguments
  - polyfill
  - 参考
  - 数组
translation_of: Web/JavaScript/Reference/Global_Objects/Array/from
---
<div>{{JSRef}}</div>

<p><code><strong>Array.from()</strong></code> 方法从一个类似数组或可迭代对象创建一个新的，浅拷贝的数组实例。</p>

<div>{{EmbedInteractiveExample("pages/js/array-from.html")}}</div>



<h2 id="语法">语法</h2>

<pre class="syntaxbox notranslate">Array.from(<em>arrayLike</em>[, <em>mapFn</em>[, <em>thisArg</em>]])
</pre>

<h3 id="参数">参数</h3>

<dl>
 <dt><code>arrayLike</code></dt>
 <dd>想要转换成数组的伪数组对象或可迭代对象。</dd>
 <dt><code>mapFn</code> {{Optional_inline}}</dt>
 <dd>如果指定了该参数，新数组中的每个元素会执行该回调函数。</dd>
 <dt><code>thisArg</code> {{Optional_inline}}</dt>
 <dd>可选参数，执行回调函数 <code>mapFn</code> 时 <code>this</code> 对象。</dd>
</dl>

<h3 id="返回值">返回值</h3>

<p>一个新的{{jsxref("Array","数组")}}实例。</p>

<h2 id="描述">描述</h2>

<p><code>Array.from()</code> 可以通过以下方式来创建数组对象：</p>

<ul>
 <li>伪数组对象（拥有一个 <code>length</code> 属性和若干索引属性的任意对象）</li>
 <li><a href="/zh-CN/docs/Web/JavaScript/Guide/iterable">可迭代对象</a>（可以获取对象中的元素,如 Map和 Set 等）</li>
</ul>

<p><code>Array.from()</code> 方法有一个可选参数 <code>mapFn</code>，让你可以在最后生成的数组上再执行一次 {{jsxref("Array.prototype.map", "map")}} 方法后再返回。也就是说<code> Array.from(obj, mapFn, thisArg) </code>就相当于<code> Array.from(obj).map(mapFn, thisArg),</code> 除非创建的不是可用的中间数组。 这对一些数组的子类<code>,</code>如 <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Typed_arrays">typed arrays</a><font face="Consolas, Liberation Mono, Courier, monospace"> 来说很重要,</font> 因为中间数组的值在调用 map() 时需要是适当的类型。</p>

<p><code>from()</code> 的 <code>length</code> 属性为 1 ，即 <code>Array.from.length === 1</code>。</p>

<p>在 ES2015 中， <code>Class</code> 语法允许我们为内置类型（比如 <code>Array</code>）和自定义类新建子类（比如叫 <code>SubArray</code>）。这些子类也会继承父类的静态方法，比如 <code>SubArray.from()</code>，调用该方法后会返回子类 <code>SubArray</code> 的一个实例，而不是 <code>Array</code> 的实例。</p>

<h2 id="示例">示例</h2>

<h3 id="从_String_生成数组">从 <code>String</code> 生成数组</h3>

<pre class="brush: js notranslate">Array.from('foo');
// [ "f", "o", "o" ]</pre>

<h3 id="从_Set_生成数组">从 <code>Set</code> 生成数组</h3>

<pre class="brush: js notranslate">const set = new Set(['foo', 'bar', 'baz', 'foo']);
Array.from(set);
// [ "foo", "bar", "baz" ]</pre>

<h3 id="从_Map_生成数组">从 <code>Map</code> 生成数组</h3>

<pre class="brush: js notranslate">const map = new Map([[1, 2], [2, 4], [4, 8]]);
Array.from(map);
// [[1, 2], [2, 4], [4, 8]]

const mapper = new Map([['1', 'a'], ['2', 'b']]);
Array.from(mapper.values());
// ['a', 'b'];

Array.from(mapper.keys());
// ['1', '2'];
</pre>

<h3 id="从类数组对象（arguments）生成数组">从类数组对象（arguments）生成数组</h3>

<pre class="brush: js notranslate">function f() {
  return Array.from(arguments);
}

f(1, 2, 3);

// [ 1, 2, 3 ]</pre>

<h3 id="在_Array.from_中使用箭头函数">在 <code>Array.from</code> 中使用箭头函数</h3>

<pre class="brush: js notranslate">// Using an arrow function as the map function to
// manipulate the elements
Array.from([1, 2, 3], x =&gt; x + x);
// [2, 4, 6]


// Generate a sequence of numbers
// Since the array is initialized with `undefined` on each position,
// the value of `v` below will be `undefined`
Array.from({length: 5}, (v, i) =&gt; i);
// [0, 1, 2, 3, 4]
</pre>

<h3 id="序列生成器指定范围">序列生成器(指定范围)</h3>

<pre class="brush: js notranslate">// Sequence generator function (commonly referred to as "range", e.g. Clojure, PHP etc)
const range = (start, stop, step) =&gt; Array.from({ length: (stop - start) / step + 1}, (_, i) =&gt; start + (i * step));

// Generate numbers range 0..4
range(0, 4, 1);
// [0, 1, 2, 3, 4]

// Generate numbers range 1..10 with step of 2
range(1, 10, 2);
// [1, 3, 5, 7, 9]

// Generate the alphabet using Array.from making use of it being ordered as a sequence
range('A'.charCodeAt(0), 'Z'.charCodeAt(0), 1).map(x =&gt; String.fromCharCode(x));
// ["A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z"]
</pre>

<h3 id="数组去重合并">数组去重合并</h3>

<pre class="brush: js notranslate">function combine(){
    let arr = [].concat.apply([], arguments);  //没有去重复的新数组
    return Array.from(new Set(arr));
}

var m = [1, 2, 2], n = [2,3,3];
console.log(combine(m,n));                     // [1, 2, 3]</pre>

<h2 id="Polyfill">Polyfill</h2>

<p>ECMA-262 第六版标准中添加了 <code>Array.from </code>。有些实现中可能尚未包括在其中。你可以通过在脚本前添加如下内容作为替代方法，以使用未原生支持的 <code>Array.from</code> 方法。该算法按照 ECMA-262 第六版中的规范实现，并假定 <code>Object</code> 和 <code>TypeError</code> 有其本身的值， <code>callback.call</code> 对应 {{jsxref("Function.prototype.call")}} 。此外，鉴于无法使用 Polyfill 实现真正的的迭代器，该实现不支持规范中定义的泛型可迭代元素。</p>

<pre class="brush: js notranslate">// Production steps of ECMA-262, Edition 6, 22.1.2.1
if (!Array.from) {
  Array.from = (function () {
    var toStr = Object.prototype.toString;
    var isCallable = function (fn) {
      return typeof fn === 'function' || toStr.call(fn) === '[object Function]';
    };
    var toInteger = function (value) {
      var number = Number(value);
      if (isNaN(number)) { return 0; }
      if (number === 0 || !isFinite(number)) { return number; }
      return (number &gt; 0 ? 1 : -1) * Math.floor(Math.abs(number));
    };
    var maxSafeInteger = Math.pow(2, 53) - 1;
    var toLength = function (value) {
      var len = toInteger(value);
      return Math.min(Math.max(len, 0), maxSafeInteger);
    };

    // The length property of the from method is 1.
    return function from(arrayLike/*, mapFn, thisArg */) {
      // 1. Let C be the this value.
      var C = this;

      // 2. Let items be ToObject(arrayLike).
      var items = Object(arrayLike);

      // 3. ReturnIfAbrupt(items).
      if (arrayLike == null) {
        throw new TypeError("Array.from requires an array-like object - not null or undefined");
      }

      // 4. If mapfn is undefined, then let mapping be false.
      var mapFn = arguments.length &gt; 1 ? arguments[1] : void undefined;
      var T;
      if (typeof mapFn !== 'undefined') {
        // 5. else
        // 5. a If IsCallable(mapfn) is false, throw a TypeError exception.
        if (!isCallable(mapFn)) {
          throw new TypeError('Array.from: when provided, the second argument must be a function');
        }

        // 5. b. If thisArg was supplied, let T be thisArg; else let T be undefined.
        if (arguments.length &gt; 2) {
          T = arguments[2];
        }
      }

      // 10. Let lenValue be Get(items, "length").
      // 11. Let len be ToLength(lenValue).
      var len = toLength(items.length);

      // 13. If IsConstructor(C) is true, then
      // 13. a. Let A be the result of calling the [[Construct]] internal method
      // of C with an argument list containing the single item len.
      // 14. a. Else, Let A be ArrayCreate(len).
      var A = isCallable(C) ? Object(new C(len)) : new Array(len);

      // 16. Let k be 0.
      var k = 0;
      // 17. Repeat, while k &lt; len… (also steps a - h)
      var kValue;
      while (k &lt; len) {
        kValue = items[k];
        if (mapFn) {
          A[k] = typeof T === 'undefined' ? mapFn(kValue, k) : mapFn.call(T, kValue, k);
        } else {
          A[k] = kValue;
        }
        k += 1;
      }
      // 18. Let putStatus be Put(A, "length", len, true).
      A.length = len;
      // 20. Return A.
      return A;
    };
  }());
}
</pre>

<h2 id="规范">规范</h2>

<table class="standard-table">
 <thead>
  <tr>
   <th scope="col">Specification</th>
   <th scope="col">Status</th>
   <th scope="col">Comment</th>
  </tr>
 </thead>
 <tbody>
  <tr>
   <td>{{SpecName('ESDraft', '#sec-array.from', 'Array.from')}}</td>
   <td>{{Spec2('ESDraft')}}</td>
   <td></td>
  </tr>
  <tr>
   <td>{{SpecName('ES2015', '#sec-array.from', 'Array.from')}}</td>
   <td>{{Spec2('ES2015')}}</td>
   <td>Initial definition.</td>
  </tr>
 </tbody>
</table>

<h2 id="浏览器兼容性">浏览器兼容性</h2>



<p>{{Compat("javascript.builtins.Array.from")}}</p>

<h2 id="相关链接">相关链接</h2>

<ul>
 <li>{{jsxref("Array")}}</li>
 <li>{{jsxref("Array.prototype.map()")}}</li>
 <li>{{jsxref("TypedArray.from()")}}</li>
</ul>