uTools-Manuals/docs/javascript/Reference/Global_Objects/WeakMap/has.html

<article id="wikiArticle">
<div></div>
<p> <code><strong>has()</strong></code> 方法根据WeakMap对象的元素中是否存在key键返回一个boolean值。</p>
<h2 id="语法">语法</h2>
<pre><code class="language-javascript"><code><em>wm</em>.has(key);</code></code></pre>
<h3 id="Parameters">Parameters</h3>
<dl>
<dt>key</dt>
<dd>必须的。用来检测WeakMap对象中是否存在元素的键为key。</dd>
</dl>
<h3 id="Return_value">Return value</h3>
<dl>
<dt>Boolean</dt>
<dd>如果指定的key存在于某个元素中则返回true，否则返回flase。</dd>
</dl>
<h2 id="例子">例子</h2>
<h3 id="使用_has方法">使用 <code>has方法</code></h3>
<pre><code  class="language-javascript">var wm = new WeakMap();
wm.set(window, "foo");

wm.has(window); // returns true
wm.has("baz");  // returns false
</code></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>
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<td><a class="external" href="https://www.ecma-international.org/ecma-262/6.0/#sec-weakmap.prototype.has" hreflang="en" lang="en" rel="noopener">ECMAScript 2015 (6th Edition, ECMA-262)<br/><small lang="zh-CN">WeakMap.prototype.has</small></a></td>
<td><span class="spec-Standard">Standard</span></td>
<td>Initial definition.</td>
</tr>
<tr>
<td><a class="external" href="https://tc39.github.io/ecma262/#sec-weakmap.prototype.has" hreflang="en" lang="en" rel="noopener">ECMAScript Latest Draft (ECMA-262)<br/><small lang="zh-CN">WeakMap.prototype.has</small></a></td>
<td><span class="spec-Draft">Draft</span></td>
<td> </td>
</tr>
</tbody>
</table>
<h2 id="浏览器兼容">浏览器兼容</h2>
<p></p><div class="blockIndicator warning"><strong><a class="external" href="https://github.com/mdn/browser-compat-data" rel="noopener">We're converting our compatibility data into a machine-readable JSON format</a></strong>.
            This compatibility table still uses the old format,
            because we haven't yet converted the data it contains.
            <strong><a class="new" href="/zh-CN/docs/MDN/Contribute/Structures/Compatibility_tables" rel="nofollow">Find out how you can help!</a></strong></div>
<div class="htab">
<a id="AutoCompatibilityTable" name="AutoCompatibilityTable"></a>
<ul>
<li class="selected"><a>Desktop</a></li>
<li><a>Mobile</a></li>
</ul>
</div><p></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><a href="/en-US/Firefox/Releases/6" title="Released on 2011-08-16.">6.0</a> (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><span style="color: #f00;">未实现</span></td>
<td>6.0 (6.0)</td>
<td><span style="color: #f00;">未实现</span></td>
<td><span style="color: #f00;">未实现</span></td>
<td>8</td>
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</tbody>
</table>
</div>
<h2 id="Firefox-特有说明">Firefox-特有说明</h2>
<ul>
<li>直到SpiderMonkey 38 (Firefox 38 / Thunderbird 38 / SeaMonkey 2.35), 这个方法在key参数不是一个对象时会抛出 <a href="Reference/Global_Objects/TypeError" title="TypeError（类型错误） 对象用来表示值的类型非预期类型时发生的错误。"><code>TypeError</code></a>。它已经从版本38后按照最新版本的ES6标准修复 (<a class="external" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1127827" rel="noopener" title="FIXED: WeakMap.get, has and delete should not throw when key param is not an object">bug 1127827</a>).</li>
</ul>
<h2 id="See_also">See also</h2>
<ul>
<li><a href="Reference/WeakMap" title="此页面仍未被本地化, 期待您的翻译!"><code>WeakMap</code></a></li>
<li><a href="Reference/Global_Objects/WeakMap/set" title="set() 方法根据指定的key和value在 WeakMap对象中添加新/更新元素。"><code>WeakMap.prototype.set()</code></a></li>
<li><a href="Reference/Global_Objects/WeakMap/get" title="get() 方法返回  WeakMap 指定的元素。"><code>WeakMap.prototype.get()</code></a></li>
</ul>
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