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+---
+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>