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+---
+title: WeakMap.prototype.get()
+slug: Web/JavaScript/Reference/Global_Objects/WeakMap/get
+translation_of: Web/JavaScript/Reference/Global_Objects/WeakMap/get
+---
+<div>{{JSRef}}</div>
+
+<p><code><strong>get()</strong></code> 方法返回  <code>WeakMap</code> 指定的元素。</p>
+
+<h2 id="语法">语法</h2>
+
+<pre class="syntaxbox"><code><em>wm</em>.get(key);</code></pre>
+
+<h3 id="参数">参数</h3>
+
+<dl>
+ <dt>key</dt>
+ <dd>必须。 想要从 <code>WeakMap </code>获取的元素的键。</dd>
+</dl>
+
+<h3 id="返回值">返回值</h3>
+
+<h3 id="返回与指定键相关联的值,如果_WeakMap_对象找不到这个键则返回_undefined。"><span style="font-size: 14px; line-height: 1.5;">返回与指定键相关联的值,如果 </span><code style="font-size: 14px; font-style: normal; font-weight: normal; line-height: 1.5;">WeakMap</code><span style="font-size: 14px; line-height: 1.5;"> 对象找不到这个键则返回 </span><code style="font-size: 14px; font-style: normal; font-weight: normal; line-height: 1.5;">undefined</code><span style="font-size: 14px; line-height: 1.5;">。</span></h3>
+
+<h2 id="例子">例子</h2>
+
+<h3 id="使用_get_方法">使用 <code>get </code>方法<code> </code></h3>
+
+<pre class="brush: js">var wm = new WeakMap();
+wm.set(window, "foo");
+
+wm.get(window); // 返回 "foo".
+wm.get("baz"); // 返回 undefined.
+</pre>
+
+<h2 id="规范">规范</h2>
+
+<table class="standard-table">
+ <tbody>
+ <tr>
+ <th scope="col">Specification</th>
+ <th scope="col">Status</th>
+ <th scope="col">Comment</th>
+ </tr>
+ <tr>
+ <td>{{SpecName('ES6', '#sec-weakmap.prototype.get', 'WeakMap.prototype.get')}}</td>
+ <td>{{Spec2('ES6')}}</td>
+ <td>Initial definition.</td>
+ </tr>
+ <tr>
+ <td>{{SpecName('ESDraft', '#sec-weakmap.prototype.get', 'WeakMap.prototype.get')}}</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>
+
+<p>{{CompatibilityTable}}</p>
+
+<div id="compat-desktop">
+<table class="compat-table">
+ <tbody>
+ <tr>
+ <th>Feature</th>
+ <th>Chrome</th>
+ <th>Firefox (Gecko)</th>
+ <th>Internet Explorer</th>
+ <th>Opera</th>
+ <th>Safari</th>
+ </tr>
+ <tr>
+ <td>Basic support</td>
+ <td>36</td>
+ <td>{{CompatGeckoDesktop("6.0")}}</td>
+ <td>11</td>
+ <td>23</td>
+ <td>7.1</td>
+ </tr>
+ </tbody>
+</table>
+</div>
+
+<div id="compat-mobile">
+<table class="compat-table">
+ <tbody>
+ <tr>
+ <th>Feature</th>
+ <th>Android</th>
+ <th>Firefox Mobile (Gecko)</th>
+ <th>IE Mobile</th>
+ <th>Opera Mobile</th>
+ <th>Safari Mobile</th>
+ </tr>
+ <tr>
+ <td>Basic support</td>
+ <td>{{CompatNo}}</td>
+ <td>{{CompatGeckoMobile("6.0")}}</td>
+ <td>{{CompatNo}}</td>
+ <td>{{CompatNo}}</td>
+ <td>8</td>
+ </tr>
+ </tbody>
+</table>
+</div>
+
+<h2 id="Firefox_中的注意事项">Firefox 中的注意事项</h2>
+
+<ul>
+ <li>Prior to SpiderMonkey 38 {{geckoRelease(38)}}, this method threw a {{jsxref("TypeError")}} when the key parameter was not an object. However, the latest ES6 standard specifies to return <code>undefined</code> instead. Furthermore, <code>WeakMap.prototype.get</code> accepted an optional second argument as a fallback value, which is not part of the standard. Both non-standard behaviors are removed in version 38 and higher ({{bug(1127827)}}).</li>
+</ul>
+
+<h2 id="相关链接">相关链接</h2>
+
+<ul>
+ <li>{{jsxref("WeakMap")}}</li>
+ <li>{{jsxref("WeakMap.set()")}}</li>
+ <li>{{jsxref("WeakMap.has()")}}</li>
+</ul>