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+---
+title: Symbol.prototype.valueOf()
+slug: Web/JavaScript/Reference/Global_Objects/Symbol/valueOf
+translation_of: Web/JavaScript/Reference/Global_Objects/Symbol/valueOf
+---
+<div>{{JSRef("Global_Objects", "Symbol")}}</div>
+
+<h2 id="Summary" name="Summary">概述</h2>
+
+<p><code><strong>valueOf()</strong></code> 方法返回当前 symbol 对象所包含的 symbol 原始值。</p>
+
+<h2 id="Syntax" name="Syntax">语法</h2>
+
+<pre class="syntaxbox"><var>symbol.valueOf();
+</var></pre>
+
+<h2 id="Description" name="Description">描述</h2>
+
+<p>在 JavaScript 中，虽然大多数类型的对象在某些操作下都会自动的隐式调用自身的 <code>valueOf()</code> 方法或者 <code>toString()</code> 方法来将自己转换成一个原始值，但 symbol 对象不会这么干，symbol 对象无法隐式转换成对应的原始值：</p>
+
+<pre class="brush: js">Object(Symbol("foo")) + "bar";
+// TypeError: can't convert symbol object to primitive
+// 无法隐式的调用 valueOf() 方法
+
+Object(Symbol("foo")).valueOf() + "bar";
+// TypeError:  can't convert symbol to string
+// 手动调用 valueOf() 方法，虽然转换成了原始值，但 symbol 原始值不能转换为字符串
+
+Object(Symbol("foo")).toString() + "bar";
+// "Symbol(foo)bar"，需要手动调用 toString() 方法才行
+</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.prototype.valueof', 'Symbol.prototype.valueOf')}}</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>
+
+<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>{{ CompatVersionUnknown() }}</td>
+   <td>{{ CompatGeckoDesktop("33.0") }}</td>
+   <td>{{ CompatNo() }}</td>
+   <td>{{ CompatNo() }}</td>
+   <td>{{ CompatNo() }}</td>
+  </tr>
+ </tbody>
+</table>
+</div>
+
+<div id="compat-mobile">
+<table class="compat-table">
+ <tbody>
+  <tr>
+   <th>Feature</th>
+   <th>Android</th>
+   <th>Chrome for 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>{{ CompatVersionUnknown() }}</td>
+   <td>{{ CompatVersionUnknown() }}</td>
+   <td>{{ CompatGeckoMobile("33.0") }}</td>
+   <td>{{ CompatNo() }}</td>
+   <td>{{ CompatNo() }}</td>
+   <td>{{ CompatNo() }}</td>
+  </tr>
+ </tbody>
+</table>
+</div>
+
+<h2 id="See_Also" name="See_Also">相关链接</h2>
+
+<ul>
+ <li>{{jsxref("Object.prototype.valueOf()")}}</li>
+</ul>