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---
title: 加法赋值 (+=)
slug: Web/JavaScript/Reference/Operators/Addition_assignment
tags:
- +=
translation_of: Web/JavaScript/Reference/Operators/Addition_assignment
---
<div>{{jsSidebar("Operators")}}</div>
<p>加法赋值操作符 (<code>+=</code>) 将右操作数的值添加到变量，并将结果分配给该变量。两个操作数的类型确定加法赋值运算符的行为。加法或串联是可能的。</p>
<div>{{EmbedInteractiveExample("pages/js/expressions-addition-assignment.html")}}</div>
<div></div>
<h2 id="Syntax">Syntax</h2>
<pre class="syntaxbox notranslate"><strong>Operator:</strong> x += y
<strong>Meaning:</strong> x = x + y</pre>
<h2 id="Examples">Examples</h2>
<h3 id="Using_addition_assignment">Using addition assignment</h3>
<pre class="brush: js notranslate">// Assuming the following variables
// foo = 'foo'
// bar = 5
// baz = true
// Number + Number -> addition
bar += 2 // 7
// Boolean + Number -> addition
baz += 1 // 2
// Boolean + Boolean -> addition
baz += false // 1
// Number + String -> concatenation
bar += 'foo' // "5foo"
// String + Boolean -> concatenation
foo += false // "foofalse"
// String + String -> concatenation
foo += 'bar' // "foobar"</pre>
<h2 id="Specifications">Specifications</h2>
<table class="standard-table">
<tbody>
<tr>
<th scope="col">Specification</th>
</tr>
<tr>
<td>{{SpecName('ESDraft', '#sec-assignment-operators', 'Assignment operators')}}</td>
</tr>
</tbody>
</table>
<h2 id="Browser_compatibility">Browser compatibility</h2>
<p>{{Compat("javascript.operators.addition_assignment")}}</p>
<h2 id="See_also">See also</h2>
<ul>
<li><a href="/en-US/docs/Web/JavaScript/Guide/Expressions_and_Operators#Assignment">Assignment operators in the JS guide</a></li>
<li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Addition">Addition operator</a></li>
</ul>
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