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+---
+title: 減算代入 (-=)
+slug: Web/JavaScript/Reference/Operators/Subtraction_assignment
+tags:
+  - Assignment operator
+  - JavaScript
+  - Language feature
+  - Operator
+  - Reference
+translation_of: Web/JavaScript/Reference/Operators/Subtraction_assignment
+---
+<div>{{jsSidebar("Operators")}}</div>
+
+<p>減算代入演算子 (<code>-=</code>) は、変数から右辺のオペランドの値を減算し、結果を変数に代入します。</p>
+
+<div>{{EmbedInteractiveExample("pages/js/expressions-subtraction-assignment.html")}}</div>
+
+<div></div>
+
+
+
+<h2 id="構文">構文</h2>
+
+<pre class="syntaxbox notranslate"><strong>Operator:</strong> x -= y
+<strong>Meaning:</strong>  x  = x - y</pre>
+
+<h2 id="例">例</h2>
+
+<h3 id="減算代入の使用">減算代入の使用</h3>
+
+<pre class="brush: js notranslate">// 次の変数を想定
+//  bar = 5
+
+bar -= 2     // 3
+bar -= 'foo' // NaN</pre>
+
+<h2 id="仕様">仕様</h2>
+
+<table class="standard-table">
+ <tbody>
+  <tr>
+   <th scope="col">仕様</th>
+  </tr>
+  <tr>
+   <td>{{SpecName('ESDraft', '#sec-assignment-operators', 'Assignment operators')}}</td>
+  </tr>
+ </tbody>
+</table>
+
+<h2 id="ブラウザーの互換性">ブラウザーの互換性</h2>
+
+
+
+<p>{{Compat("javascript.operators.subtraction_assignment")}}</p>
+
+<h2 id="関連項目">関連項目</h2>
+
+<ul>
+ <li><a href="/docs/Web/JavaScript/Guide/Expressions_and_Operators#Assignment">代入演算子</a></li>
+ <li><a href="/docs/Web/JavaScript/Reference/Operators/Subtraction">減算演算子</a></li>
+</ul>