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+---
+title: Array.prototype.flatMap()
+slug: Web/JavaScript/Reference/Global_Objects/Array/flatMap
+tags:
+  - Array
+  - JavaScript
+  - Method
+  - Prototype
+  - Reference
+translation_of: Web/JavaScript/Reference/Global_Objects/Array/flatMap
+---
+<div>{{JSRef}}</div>
+
+<p><code><strong>flatMap()</strong></code> 方法首先使用映射函数映射每个元素，然后将结果压缩成一个新数组。它与 <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map">map</a> 连着深度值为1的 <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/flat">flat</a> 几乎相同，但 <code>flatMap</code> 通常在合并成一种方法的效率稍微高一些。</p>
+
+<p class="hidden">\{{EmbedInteractiveExample("pages/js/array-flatmap.html")}}</p>
+
+<p class="hidden">此交互式示例的源代码存储在GitHub存储库中。如果您想要为交互式示例项目做出贡献，请复制https：//github.com/mdn/interactive-examples，并向我们发送 pull request。</p>
+
+<h2 id="语法">语法</h2>
+
+<pre class="syntaxbox notranslate"><var>var new_array = arr</var>.flatMap(function <var>callback(currentValue[, index[, array]]) {
+    // return element for new_array
+}</var>[, <var>thisArg</var>])</pre>
+
+<h3 id="参数">参数</h3>
+
+<dl>
+ <dt><code>callback</code></dt>
+ <dd>可以生成一个新数组中的元素的函数，可以传入三个参数：
+ <dl>
+  <dt></dt>
+  <dt><code>currentValue</code></dt>
+  <dd>当前正在数组中处理的元素</dd>
+  <dt><code>index</code>{{optional_inline}}</dt>
+  <dd>可选的。数组中正在处理的当前元素的索引。</dd>
+  <dt><code>array</code>{{optional_inline}}</dt>
+  <dd>可选的。被调用的 <code>map</code> 数组</dd>
+ </dl>
+ </dd>
+ <dt><code>thisArg</code>{{optional_inline}}</dt>
+ <dd>可选的。执行 <code>callback</code> 函数时 使用的<code>this</code> 值。</dd>
+</dl>
+
+<h3 id="返回值">返回值</h3>
+
+<p> 一个新的数组，其中每个元素都是回调函数的结果，并且结构深度 <code>depth</code> 值为1。</p>
+
+<h2 id="描述">描述</h2>
+
+<p>有关回调函数的详细描述，请参见 {{jsxref("Array.prototype.map()")}} 。 <code>flatMap</code> 方法与 <code><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map">map</a></code> 方法和深度depth为1的 <code><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/flat">flat</a></code> 几乎相同.</p>
+
+<h2 id="示例">示例</h2>
+
+<h3 id="map_与_flatMap"><code>map()</code> 与 <code>flatMap()</code></h3>
+
+<pre class="brush: js notranslate">var arr1 = <span class="js source"><span class="function-call js meta"><span class="js meta"><span class="brace js meta square"><span>[</span></span><span class="constant decimal js numeric"><span>1</span></span><span class="comma delimiter js meta object"><span>,</span></span><span> </span><span class="brace js meta square"><span>2, 3, 4];
+
+arr1.map(</span></span></span></span></span>x =&gt; [x * 2]<span class="js source"><span class="function-call js meta"><span class="js meta"><span class="brace js meta square"><span>);</span></span></span></span></span>
+// [[2], [4], [6], [8]]
+
+arr1.flatMap(x =&gt; [x * 2]<span class="js source"><span class="function-call js meta"><span class="js meta"><span class="brace js meta square"><span>);
+// [2, 4, 6, 8]</span></span></span></span></span>
+
+// <code>only one level is flatt</code><code>ened</code>
+arr1.flatMap(x =&gt; [[x * 2]]);
+// [[2], [4], [6], [8]]</pre>
+
+<p>虽然上面的代码使用 map 和 flatMap 好像都可以，但这只能展示如何使用 flatMap。</p>
+
+<p>所以，为了更好的展示 flatMap 的作用，下面我们将包含几句话的数组拆分成单个词组成的新数组。</p>
+
+<pre class="notranslate"><code>let arr1 = ["it's Sunny in", "", "California"];
+
+arr1.map(x =&gt; x.split(" "));
+// [["it's","Sunny","in"],[""],["California"]]
+
+arr1.flatMap(x =&gt; x.split(" "));
+// ["it's","Sunny","in", "", "California"]</code></pre>
+
+<p>注意，输出列表长度可以不同于输入列表长度。</p>
+
+<h3 id="在一个_map_期间增加或去除一些项">在一个 <code>map()</code> 期间增加或去除一些项</h3>
+
+<p><code>flatMap</code> 能用于在map期间增删项目（也就是修改items的数量）。换句话说，它允许你遍历很多项使之成为另一些项（靠分别把它们放进去来处理），而不是总是一对一。 从这个意义上讲，它的作用类似于 <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter">filter</a>的对立面。只需返回一个1项元素数组以保留该项，返回一个多元素数组以添加项，或返回一个0项元素数组以删除该项。</p>
+
+<pre class="notranslate"><code>// Let's say we want to remove all the negative numbers and split the odd numbers into an even number and a 1
+let a = [5, 4, -3, 20, 17, -33, -4, 18]
+//       |\  \  x   |  | \   x   x   |
+//      [4,1, 4,   20, 16, 1,       18]
+
+a.flatMap( (n) =&gt;
+  (n &lt; 0) ?      [] :
+  (n % 2 == 0) ? [n] :
+                 [n-1, 1]
+)
+
+// expected output: [4, 1, 4, 20, 16, 1, 18]</code></pre>
+
+<h2 id="替代方案">替代方案</h2>
+
+<h3 id="reduce_与_concat"><code>reduce()</code> 与 <code>concat()</code></h3>
+
+<pre class="notranslate"><code>var arr = [1, 2, 3, 4];
+
+arr.flatMap(x =&gt; [x, x * 2]);
+// is equivalent to
+arr.reduce((acc, x) =&gt; acc.concat([x, x * 2]), []);
+// [1, 2, 2, 4, 3, 6, 4, 8]</code></pre>
+
+<p>请注意，这是低效的，并且应该避免大型阵列：在每次迭代中，它创建一个必须被垃圾收集的新临时数组，并且它将元素从当前的累加器数组复制到一个新的数组中，而不是将新的元素添加到现有的数组中。</p>
+
+<div class="hidden">
+<p>Please do not add polyfills on this article. For reference, please check: <a href="https://discourse.mozilla.org/t/mdn-rfc-001-mdn-wiki-pages-shouldnt-be-a-distributor-of-polyfills/24500">https://discourse.mozilla.org/t/mdn-rfc-001-mdn-wiki-pages-shouldnt-be-a-distributor-of-polyfills/24500</a></p>
+</div>
+
+<h2 id="规范">规范</h2>
+
+<table class="standard-table">
+ <tbody>
+  <tr>
+   <td>Specification</td>
+   <td>Status</td>
+   <td>Comment</td>
+  </tr>
+  <tr>
+   <td>{{SpecName('ESDraft', '#sec-array.prototype.flatmap', 'Array.prototype.flatMap')}}</td>
+   <td>{{Spec2('ESDraft')}}</td>
+   <td></td>
+  </tr>
+ </tbody>
+</table>
+
+<h2 id="浏览器兼容性">浏览器兼容性</h2>
+
+<div class="hidden">
+<p>The compatibility table in this page is generated from structured data. If you'd like to contribute to the data, please check out <a href="https://github.com/mdn/browser-compat-data">https://github.com/mdn/browser-compat-data</a> and send us a pull request.</p>
+</div>
+
+<p>{{Compat("javascript.builtins.Array.flatMap")}}</p>
+
+<h2 id="参见">参见</h2>
+
+<ul>
+ <li>{{jsxref("Array.prototype.flat()")}}</li>
+ <li>{{jsxref("Array.prototype.map()")}}</li>
+ <li>{{jsxref("Array.prototype.reduce()")}}</li>
+ <li>{{jsxref("Array.prototype.concat()")}}</li>
+</ul>