---
title: 求幂 (**)
slug: Web/JavaScript/Reference/Operators/Exponentiation
tags:
  - JavaScript
  - 参考
  - 语言特征
  - 运算符
translation_of: Web/JavaScript/Reference/Operators/Exponentiation
---
<div>{{jsSidebar("Operators")}}</div>

<p><font><font>求幂运算符（</font></font><code>**</code><font><font>）返回将第一个操作数加到第二个操作数</font><font>的幂</font><font>的结果。</font><font>它等效于</font></font><code>Math.pow</code><font><font>，不同之处在于它也接受BigInts作为操作数。</font></font></p>

<div>{{EmbedInteractiveExample("pages/js/expressions-exponentiation.html")}}</div>



<h2 id="语法">语法</h2>

<pre class="syntaxbox notranslate"><strong>Operator:</strong> <var>var1</var> ** <var>var2</var>
</pre>

<h2 id="简介">简介</h2>

<p>求幂运算符是是<strong>右结合的</strong>: <code><var>a</var> ** <var>b</var> ** <var>c</var></code> 等于 <code><var>a</var> ** (<var>b</var> ** <var>c</var>)</code>.</p>

<p>在大多数语言里，比如PHP、Python等那些有一个幂运算符 (<code>**</code>) 的语言，幂运算符被定义有一个比一元运算符，比如一元的 <code>+</code> 和一元的 <code>-</code> 更高的运算顺序，但有一些例外。在Bash语言里，<code>**</code> 运算符被定义有一个比一元运算符更低的运算顺序。</p>

<p>在JavaScript里，你不可能写出一个不明确的求幂表达式。这就是说，你不能立刻将一个一元运算符（<code>+/-/~/!/delete/void/typeof</code>）放在基数前，这样做只会导致一个语法错误。</p>

<pre class="brush: js notranslate">-2 ** 2;
// 4 in Bash, -4 in other languages.
// This is invalid in JavaScript, as the operation is ambiguous.


-(2 ** 2);
// -4 in JavaScript and the author's intention is unambiguous.
</pre>

<p>注意有些编程语言用扬抑符 <kbd>^</kbd> 做乘方运算，但是JavaScript将这个符号作为了<a href="/en-US/docs/Web/JavaScript/Reference/Operators/Bitwise_Operators#Bitwise_XOR">XOR位逻辑运算符</a>。</p>

<h2 id="例子">例子</h2>

<h3 id="基本求幂">基本求幂</h3>

<pre class="brush: js notranslate">2 ** 3   // 8
3 ** 2   // 9
3 ** 2.5 // 15.588457268119896
10 ** -1 // 0.1
NaN ** 2 // NaN
</pre>

<h3 id="结合">结合</h3>

<pre class="brush: js notranslate">2 ** 3 ** 2   // 512
2 ** (3 ** 2) // 512
(2 ** 3) ** 2 // 64</pre>

<h3 id="与一元运算符的用法">与一元运算符的用法</h3>

<p>取求幂表达式的值的相反数：</p>

<pre class="brush: js notranslate">-(2 ** 2) // -4
</pre>

<p>将求幂表达式的底数转化为一个负数：</p>

<pre class="brush: js notranslate">(-2) ** 2 // 4
</pre>

<h2 id="规范">规范</h2>

<table class="standard-table">
 <tbody>
  <tr>
   <th scope="col">Specification</th>
  </tr>
  <tr>
   <td>{{SpecName('ESDraft', '#sec-exp-operator', 'Exponentiation operator')}}</td>
  </tr>
 </tbody>
</table>

<h2 id="浏览器支持">浏览器支持</h2>



<p>{{Compat("javascript.operators.exponentiation")}}</p>

<h2 id="See_also">See also</h2>

<ul>
 <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Addition">Addition operator</a></li>
 <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Subtraction">Subtraction operator</a></li>
 <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Division">Division operator</a></li>
 <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Multiplication">Multiplication operator</a></li>
 <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Remainder">Remainder operator</a></li>
 <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Increment">Increment operator</a></li>
 <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Decrement">Decrement operator</a></li>
 <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Unary_negation">Unary negation operator</a></li>
 <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Unary_plus">Unary plus operator</a></li>
</ul>

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