---
title: Symbol.keyFor()
slug: Web/JavaScript/Reference/Global_Objects/Symbol/keyFor
translation_of: Web/JavaScript/Reference/Global_Objects/Symbol/keyFor
---
<div>{{JSRef("Global_Objects", "Symbol")}}</div>

<h2 id="Summary">概述</h2>

<p><code><strong>Symbol.keyFor(sym)</strong></code> 方法用来获取全局symbol 注册表中与某个 symbol 关联的键。</p>

<h2 id="Syntax">语法</h2>

<pre class="syntaxbox"><var>Symbol.keyFor(sym)</var>;</pre>

<h3 id="参数">参数</h3>

<dl>
 <dt>sym</dt>
 <dd>必选参数，需要查找键值的某个 Symbol 。</dd>
</dl>

<h3 id="返回值">返回值</h3>

<p>如果全局注册表中查找到该symbol，则返回该symbol的key值，返回值为字符串类型。否则返回undefined</p>

<h2 id="示例">示例</h2>

<pre class="brush: js">// 创建一个全局 Symbol
var globalSym = Symbol.for("foo");
Symbol.keyFor(globalSym); // "foo"

var localSym = Symbol();
Symbol.keyFor(localSym); // undefined，

// 以下Symbol不是保存在全局Symbol注册表中
Symbol.keyFor(Symbol.iterator) // 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-symbol.keyfor', 'Symbol.keyFor')}}</td>
   <td>{{Spec2('ES6')}}</td>
   <td>Initial definition.</td>
  </tr>
 </tbody>
</table>

<h2 id="浏览器兼容性">浏览器兼容性</h2>

{{Compat}}

<h2 id="See_Also">相关链接</h2>

<ul>
 <li>{{jsxref("Symbol.prototype.for()")}}</li>
</ul>