path: root/files/zh-cn/conflicting/web/javascript/reference/operators_8d54701de06af40a7c984517cbe87b3e/index.html

---
title: 赋值运算符
slug: >-
  conflicting/Web/JavaScript/Reference/Operators_8d54701de06af40a7c984517cbe87b3e
tags:
  - JavaScript
  - 运算符
translation_of: Web/JavaScript/Reference/Operators#Assignment_operators
translation_of_original: Web/JavaScript/Reference/Operators/Assignment_Operators
original_slug: Web/JavaScript/Reference/Operators/Assignment_Operators
---
<div>{{jsSidebar("Operators")}}</div>

<p>赋值运算符（<strong>assignment operator</strong>）基于右值（right operand）的值，给左值（left operand）赋值。</p>

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

<p class="hidden">本文的交互示例的源代码存储在GithHub仓库。如果你愿意贡献更多交互示例，请克隆仓库 <a href="https://github.com/mdn/interactive-examples">https://github.com/mdn/interactive-examples</a> 并提交 pull request.</p>

<h2 id="概述">概述</h2>

<p>基本的赋值运算符是等号（<code>=</code>），该运算符把它右边的运算值赋给左边。即，<code>x = y</code> 把 <code>y</code> 的值赋给 <code>x</code>。 其他的赋值运算符通常是标准运算符的简写形式，如下面的定义与示例。 </p>

<table class="standard-table">
 <tbody>
  <tr>
   <th>名称</th>
   <th>简写形式</th>
   <th>含义</th>
  </tr>
  <tr>
   <td><a href="#Assignment">赋值（Assignment）</a></td>
   <td><code>x = y</code></td>
   <td><code>x = y</code></td>
  </tr>
  <tr>
   <td><a href="#Addition_assignment">加赋值（Addition assignment）</a></td>
   <td><code>x += y</code></td>
   <td><code>x = x + y</code></td>
  </tr>
  <tr>
   <td><a href="#Subtraction_assignment">减赋值（Subtraction assignment）</a></td>
   <td><code>x -= y</code></td>
   <td><code>x = x - y</code></td>
  </tr>
  <tr>
   <td><a href="#Multiplication_assignment">乘赋值（Multiplication assigment）</a></td>
   <td><code>x *= y</code></td>
   <td><code>x = x * y</code></td>
  </tr>
  <tr>
   <td><a href="#Division_assignment">除赋值（Division assignment）</a></td>
   <td><code>x /= y</code></td>
   <td><code>x = x / y</code></td>
  </tr>
  <tr>
   <td><a href="#Remainder_assignment">模赋值（Remainder assignment）</a></td>
   <td><code>x %= y</code></td>
   <td><code>x = x % y</code></td>
  </tr>
  <tr>
   <td><a href="#Exponentiation_assignment">指数赋值（Exponentiation assignment）</a></td>
   <td><code>x **= y</code></td>
   <td><code>x = x ** y</code></td>
  </tr>
  <tr>
   <td><a href="#Left_shift_assignment">左移赋值（Left shift assignment）</a></td>
   <td><code>x &lt;&lt;= y</code></td>
   <td><code>x = x &lt;&lt; y</code></td>
  </tr>
  <tr>
   <td><a href="#Right_shift_assignment">右移赋值（Right shift assignment）</a></td>
   <td><code>x &gt;&gt;= y</code></td>
   <td><code>x = x &gt;&gt; y</code></td>
  </tr>
  <tr>
   <td><a href="#Unsigned_right_shift_assignment">无符号右移赋值（Unsigned right shift assignment）</a></td>
   <td><code>x &gt;&gt;&gt;= y</code></td>
   <td><code>x = x &gt;&gt;&gt; y</code></td>
  </tr>
  <tr>
   <td><a href="#Bitwise_AND_assignment">按位与赋值（Bitwise AND assignment）</a></td>
   <td><code>x &amp;= y</code></td>
   <td><code>x = x &amp; y</code></td>
  </tr>
  <tr>
   <td><a href="#Bitwise_XOR_assignment">按位异或赋值（Bitwise XOR assignment）</a></td>
   <td><code>x ^= y</code></td>
   <td><code>x = x ^ y</code></td>
  </tr>
  <tr>
   <td><a href="#Bitwise_OR_assignment">按位或赋值（Bitwise OR assignment）</a></td>
   <td><code>x |= y</code></td>
   <td><code>x = x | y</code></td>
  </tr>
 </tbody>
</table>

<h2 id="赋值"><a name="Assignment">赋值</a></h2>

<p>简单的赋值运算符，把一个值赋给一个变量。为了把一个值赋给多个变量，可以以链式使用赋值运算符。参考下例：</p>

<h4 id="语法">语法</h4>

<pre class="syntaxbox"><strong>Operator:</strong> x = y
</pre>

<h4 id="示例">示例</h4>

<pre class="brush: js">// Assuming the following variables
//  x = 5
//  y = 10
//  z = 25

x = y     // x is 10
x = y = z // x, y and z are all 25
</pre>

<h3 id="加赋值（Addition_assignment）"><a name="Addition_assignment">加赋值（Addition assignment）</a></h3>

<p>加赋值运算符把一个右值与一个变量相加，然后把相加的结果赋给该变量。两个操作数的类型决定了加赋值运算符的行为。算术相加或字符串连接都有可能。更多细节参考 {{jsxref("Operators/Arithmetic_Operators", "addition operator", "#Addition", 1)}}。</p>

<h4 id="语法_2">语法</h4>

<pre class="syntaxbox"><strong>Operator:</strong> x += y
<strong>Meaning:</strong>  x  = x + y
</pre>

<h4 id="示例_2">示例</h4>

<pre class="brush: js">// 定义下列变量
//  foo = 'foo'
//  bar = 5
//  baz = true


// Number + Number -&gt; addition
bar += 2 // 7

// Boolean + Number -&gt; addition
baz += 1 // 2

// Boolean + Boolean -&gt; addition
baz += false // 1

// Number + String -&gt; concatenation
bar += 'foo' // "5foo"

// String + Boolean -&gt; concatenation
foo += false // "foofalse"

// String + String -&gt; concatenation
foo += 'bar' // "foobar"
</pre>

<h3 id="减赋值（Subtraction_assignment）"><a name="Subtraction_assignment">减赋值（Subtraction assignment）</a></h3>

<p>减赋值运算符使一个变量减去右值，然后把结果赋给该变量。更多细节查看 {{jsxref("Operators/Arithmetic_Operators", "subtraction operator", "#Subtraction", 1)}} 。</p>

<h4 id="语法_3">语法</h4>

<pre class="syntaxbox"><strong>Operator:</strong> x -= y
<strong>Meaning:</strong>  x  = x - y
</pre>

<h4 id="示例_3">示例</h4>

<pre class="brush: js">// 假定已定义了下面的变量
//  bar = 5

bar -= 2     // 3
bar -= "foo" // NaN
</pre>

<h3 id="乘赋值（Multiplication_assignment）"><a name="Multiplication_assignment">乘赋值（Multiplication assignment）</a></h3>

<p>乘赋值运算符使一个变量乘以右值，然后把相成的结果赋给该变量。更多细节查看 {{jsxref("Operators/Arithmetic_Operators", "multiplication operator", "#Multiplication", 1)}}。</p>

<h4 id="语法_4">语法</h4>

<pre class="syntaxbox"><strong>Operator:</strong> x *= y
<strong>Meaning:</strong>  x  = x * y
</pre>

<h4 id="示例_4">示例</h4>

<pre class="brush: js">// 假定已定义了下面的变量
//  bar = 5

bar *= 2     // 10
bar *= 'foo' // NaN
</pre>

<h3 id="除赋值（Division_assignment）"><a name="Division_assignment">除赋值（Division assignment）</a></h3>

<p>除赋值运算符使一个变量除以右值，然后把结果赋给该变量。更多细节查看 {{jsxref("Operators/Arithmetic_Operators", "division operator", "#Division", 1)}}。</p>

<h4 id="语法_5">语法</h4>

<pre class="syntaxbox"><strong>Operator:</strong> x /= y
<strong>Meaning:</strong>  x  = x / y
</pre>

<h4 id="示例_5">示例</h4>

<pre class="brush: js">// 假定已定义了下面的变量
//  bar = 5

bar /= 2     // 2.5
bar /= "foo" // NaN
bar /= 0     // Infinity
</pre>

<h3 id="模赋值（Remainder_assignment）"><a name="Remainder_assignment">模赋值（Remainder assignment）</a></h3>

<p>模赋值运算符使一个变量除以右值，然后把余数赋给该变量。更多细节查看 {{jsxref("Operators/Arithmetic_Operators", "remainder operator", "#Remainder", 1)}}。</p>

<h4 id="语法_6">语法</h4>

<pre class="syntaxbox"><strong>Operator:</strong> x %= y
<strong>Meaning:</strong>  x  = x % y
</pre>

<h4 id="示例_6">示例</h4>

<pre class="brush: js">// Assuming the following variable
//  bar = 5

bar %= 2     // 1
bar %= 'foo' // NaN
bar %= 0     // NaN
</pre>

<h3 id="指数赋值（Exponentiation_assignment）"><a id="Exponentiation_assignment" name="Exponentiation_assignment">指数赋值（Exponentiation assignment）</a></h3>

<p>指数赋值运算符使一个变量为底数、以右值为指数的指数运算（乘方）结果赋给该变量。更多细节查看 {{jsxref("Operators/Arithmetic_Operators", "算术运算符", "#Exponentiation", 1)}}。</p>

<h4 id="语法_7">语法</h4>

<pre class="syntaxbox"><strong>语法:</strong> x **= y
<strong>含义:</strong>  x  = x ** y
</pre>

<h4 id="示例_7">示例</h4>

<pre class="brush: js">// Assuming the following variable
//  bar = 5

bar **= 2     // 25
bar **= 'foo' // NaN</pre>

<h3 id="左移赋值（Left_shift_assignment）"><a name="Left_shift_assignment">左移赋值（Left shift assignment）</a></h3>

<p>左移赋值运算符使变量向左移动指定位数的比特位，然后把结果赋给该变量。更多细节查看 {{jsxref("Operators/Bitwise_Operators", "left shift operator", "#Left_shift", 1)}}。</p>

<h4 id="语法_8">语法</h4>

<pre class="syntaxbox"><strong>Operator:</strong> x &lt;&lt;= y
<strong>Meaning:</strong>  x   = x &lt;&lt; y
</pre>

<h4 id="示例_8">示例</h4>

<pre class="brush: js">var bar = 5; //  (00000000000000000000000000000101)
bar &lt;&lt;= 2; // 20 (00000000000000000000000000010100)
</pre>

<h3 id="右移赋值（Right_shift_assignment）"><a name="Right_shift_assignment">右移赋值（Right shift assignment）</a></h3>

<p>右移赋值运算符使变量向右移指定位数的比特位，然后把结果赋给该变量。更多细节查看 {{jsxref("Operators/Bitwise_Operators", "right shift operator", "#Right_shift", 1)}}。</p>

<h4 id="语法_9">语法</h4>

<pre class="syntaxbox"><strong>Operator:</strong> x &gt;&gt;= y
<strong>Meaning:</strong>  x   = x &gt;&gt; y
</pre>

<h4 id="示例_9">示例</h4>

<pre class="brush: js">var bar = 5; //   (00000000000000000000000000000101)
bar &gt;&gt;= 2;   // 1 (00000000000000000000000000000001)

var bar = -5; //    (-00000000000000000000000000000101)
bar &gt;&gt;= 2;  // -2 (-00000000000000000000000000000010)
</pre>

<h3 id="无符号右移赋值（Unsigned_right_shift_assignment）"><a name="Unsigned_right_shift_assignment">无符号右移赋值（Unsigned right shift assignment）</a></h3>

<p>无符号右移赋值运算符向右移动指定数量的比特位，然后把结果赋给变量。更多细节查看 {{jsxref("Operators/Bitwise_Operators", " unsigned right shift operator", "#Unsigned_right_shift", 1)}}。</p>

<h4 id="语法_10">语法</h4>

<pre class="syntaxbox"><strong>Operator:</strong> x &gt;&gt;&gt;= y
<strong>Meaning:</strong>  x    = x &gt;&gt;&gt; y
</pre>

<h4 id="示例_10">示例</h4>

<pre class="brush: js">var bar = 5; //   (00000000000000000000000000000101)
bar &gt;&gt;&gt;= 2;  // 1 (00000000000000000000000000000001)

var bar = -5; // (-00000000000000000000000000000101)
bar &gt;&gt;&gt;= 2; // 1073741822 (00111111111111111111111111111110)</pre>

<h3 id="按位与赋值（Bitwise_AND_assignment）"><a name="Bitwise_AND_assignment">按位与赋值（Bitwise AND assignment）</a></h3>

<p>按位与赋值运算符使用两个操作值的二进制表示，执行按位与运算，并把结果赋给变量。更多细节查看 {{jsxref("Operators/Bitwise_Operators", "bitwise AND operator", "#Bitwise_AND", 1)}}。</p>

<h4 id="语法_11">语法</h4>

<pre class="syntaxbox"><strong>Operator:</strong> x &amp;= y
<strong>Meaning:</strong>  x  = x &amp; y
</pre>

<h4 id="示例_11">示例</h4>

<pre class="brush: js">var bar = 5;
// 5:     00000000000000000000000000000101
// 2:     00000000000000000000000000000010
bar &amp;= 2; // 0
</pre>

<h3 id="按位异或赋值（Bitwise_XOR_assignment）"><a name="Bitwise_XOR_assignment">按位异或赋值（Bitwise XOR assignment）</a></h3>

<p>按位异或赋值运算符使用两个操作值的二进制表示，执行二进制异或运算，并把结果赋给变量。更多细节查看 {{jsxref("Operators/Bitwise_Operators", "bitwise XOR operator", "#Bitwise_XOR", 1)}}。</p>

<h4 id="语法_12">语法</h4>

<pre class="syntaxbox"><strong>Operator:</strong> x ^= y
<strong>Meaning:</strong>  x  = x ^ y
</pre>

<h4 id="示例_12">示例</h4>

<pre class="brush: js">var bar = 5;
bar ^= 2; // 7
// 5: 00000000000000000000000000000101
// 2: 00000000000000000000000000000010
// -----------------------------------
// 7: 00000000000000000000000000000111
</pre>

<h3 id="按位或赋值（Bitwise_OR_assignment）"><a name="Bitwise_OR_assignment">按位或赋值（Bitwise OR assignment）</a></h3>

<p>按位或赋值运算符使用两个操作值的二进制表示，执行按位或运算，并把结果赋给变量。更多细节查看 {{jsxref("Operators/Bitwise_Operators", "bitwise OR operator", "#Bitwise_OR", 1)}}。</p>

<h4 id="语法_13">语法</h4>

<pre class="syntaxbox"><strong>Operator:</strong> x |= y
<strong>Meaning:</strong>  x  = x | y
</pre>

<h4 id="示例_13">示例</h4>

<pre class="brush: js">var bar = 5;
bar |= 2; // 7
// 5: 00000000000000000000000000000101
// 2: 00000000000000000000000000000010
// -----------------------------------
// 7: 00000000000000000000000000000111
</pre>

<h2 id="示例_14">示例</h2>

<h3 id="带有赋值运算符的左值（Left_operand）">带有赋值运算符的左值（Left operand）</h3>

<p>在某些不常见的情况下，赋值运算符（如<code> x += y</code>）并不等同于表达式（ <code>x = x + y</code>）。当一个赋值运算符的左值包含有一个赋值运算符时，左值只会被求值一次。例如：</p>

<pre class="brush: js">a[i++] += 5         // i 执行一次求值
a[i++] = a[i++] + 5 // i 执行两次求值
</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('ESDraft', '#sec-assignment-operators', 'Assignment operators')}}</td>
   <td>{{Spec2('ESDraft')}}</td>
   <td></td>
  </tr>
  <tr>
   <td>{{SpecName('ES2015', '#sec-assignment-operators', 'Assignment operators')}}</td>
   <td>{{Spec2('ES2015')}}</td>
   <td></td>
  </tr>
  <tr>
   <td>{{SpecName('ES5.1', '#sec-11.13', 'Assignment operators')}}</td>
   <td>{{Spec2('ES5.1')}}</td>
   <td></td>
  </tr>
  <tr>
   <td>{{SpecName('ES1', '#sec-11.13', 'Assignment operators')}}</td>
   <td>{{Spec2('ES1')}}</td>
   <td>Initial definition.</td>
  </tr>
 </tbody>
</table>

<h2 id="浏览器兼容性">浏览器兼容性</h2>

<div class="hidden">该兼容表是由结构化数据生成。如果你愿意贡献数据，请克隆仓库 <a href="https://github.com/mdn/browser-compat-data">https://github.com/mdn/browser-compat-data</a> 并提交 pull request.</div>

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

<h2 id="相关链接">相关链接</h2>

<ul>
 <li><a href="/zh-CN/docs/Web/JavaScript/Reference/Operators/Arithmetic_Operators">算术运算符</a></li>
</ul>