---
title: Subtraction assignment (-=)
slug: Web/JavaScript/Reference/Operators/Subtraction_assignment
translation_of: Web/JavaScript/Reference/Operators/Subtraction_assignment
---
<div>{{jsSidebar("Operators")}}</div>

<p>The subtraction assignment operator (<code>-=</code>) subtracts the value of the right operand from a variable and assigns the result to the variable.</p>

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

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<h2 id="语法">语法</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_subtraction_assignment">Using subtraction assignment</h3>

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

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

<h2 id="Specifications">Specifications</h2>

<table class="standard-table">
 <tbody>
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   <th scope="col">Specification</th>
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   <td>{{SpecName('ESDraft', '#sec-assignment-operators', 'Assignment operators')}}</td>
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 </tbody>
</table>

<h2 id="Browser_compatibility">Browser compatibility</h2>



<p>{{Compat("javascript.operators.subtraction_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/Subtraction">Subtraction operator</a></li>
</ul>

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