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---
title: Math.abs()
slug: Web/JavaScript/Reference/Global_Objects/Math/abs
tags:
- JavaScript
- Math
- Method
- Reference
translation_of: Web/JavaScript/Reference/Global_Objects/Math/abs
---
<div>{{JSRef}}</div>
<p><strong><code>Math.abs()</code></strong> 函式會回傳一個數字的絕對值，即為：</p>
<p><math display="block"><semantics><mrow><mstyle mathvariant="monospace"><mrow><mo lspace="0em" rspace="thinmathspace">Math.abs</mo><mo stretchy="false">(</mo><mi>x</mi><mo stretchy="false">)</mo></mrow></mstyle><mo>=</mo><mrow><mo stretchy="false">|</mo><mi>x</mi><mo stretchy="false">|</mo></mrow><mo>=</mo><mrow><mo>{</mo><mtable columnalign="left left"><mtr><mtd><mi>x</mi></mtd><mtd><mtext>if</mtext><mspace width="1em"></mspace><mi>x</mi><mo>></mo><mn>0</mn></mtd></mtr><mtr><mtd><mi>0</mi></mtd><mtd><mtext>if</mtext><mspace width="1em"></mspace><mi>x</mi><mo>=</mo><mn>0</mn></mtd></mtr><mtr><mtd><mo>-</mo><mi>x</mi></mtd><mtd><mtext>if</mtext><mspace width="1em"></mspace><mi>x</mi><mo><</mo><mn>0</mn></mtd></mtr></mtable></mrow></mrow><annotation encoding="TeX">{\mathtt{\operatorname{Math.abs}(x)}} = {|x|} = \begin{cases} x & \text{if} \quad x \geq 0 \\ x & \text{if} \quad x < 0 \end{cases} </annotation></semantics></math></p>
<div>{{EmbedInteractiveExample("pages/js/math-abs.html")}}</div>
<h2 id="語法">語法</h2>
<pre class="syntaxbox">Math.abs(<var>x</var>)</pre>
<h3 id="參數">參數</h3>
<dl>
<dt><code>x</code></dt>
<dd>一個數字。</dd>
</dl>
<h3 id="回傳值">回傳值</h3>
<p>給定數字的絕對值。</p>
<h2 id="描述">描述</h2>
<p>Because <code>abs()</code> is a static method of <code>Math</code>, you always use it as <code>Math.abs()</code>, rather than as a method of a <code>Math</code> object you created (<code>Math</code> is not a constructor).</p>
<h2 id="範例">範例</h2>
<h3 id="Math.abs()_的行為"><code>Math.abs()</code> 的行為</h3>
<p>Passing an empty object, an array with more than one member, a non-numeric string or {{jsxref("undefined")}}/empty variable returns {{jsxref("NaN")}}. Passing {{jsxref("null")}}, an empty string or an empty array returns 0.</p>
<pre class="brush: js" dir="rtl">Math.abs('-1'); // 1
Math.abs(-2); // 2
Math.abs(null); // 0
Math.abs(''); // 0
Math.abs([]); // 0
Math.abs([2]); // 2
Math.abs([1,2]); // NaN
Math.abs({}); // NaN
Math.abs('string'); // NaN
Math.abs(); // NaN
</pre>
<h2 id="規範">規範</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('ES1')}}</td>
<td>{{Spec2('ES1')}}</td>
<td>Initial definition. Implemented in JavaScript 1.0.</td>
</tr>
<tr>
<td>{{SpecName('ES5.1', '#sec-15.8.2.1', 'Math.abs')}}</td>
<td>{{Spec2('ES5.1')}}</td>
<td> </td>
</tr>
<tr>
<td>{{SpecName('ES6', '#sec-math.abs', 'Math.abs')}}</td>
<td>{{Spec2('ES6')}}</td>
<td> </td>
</tr>
<tr>
<td>{{SpecName('ESDraft', '#sec-math.abs', 'Math.abs')}}</td>
<td>{{Spec2('ESDraft')}}</td>
<td> </td>
</tr>
</tbody>
</table>
<h2 id="瀏覽器相容性">瀏覽器相容性</h2>
<p class="hidden">The compatibility table in this page is generated from structured data. If you'd like to contribute to the data, please check out <a href="https://github.com/mdn/browser-compat-data">https://github.com/mdn/browser-compat-data</a> and send us a pull request.</p>
<p>{{Compat("javascript.builtins.Math.abs")}}</p>
<h2 id="參見">參見</h2>
<ul>
<li>{{jsxref("Math.ceil()")}}</li>
<li>{{jsxref("Math.floor()")}}</li>
<li>{{jsxref("Math.round()")}}</li>
<li>{{jsxref("Math.sign()")}}</li>
<li>{{jsxref("Math.trunc()")}}</li>
</ul>
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