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---
title: Math.abs()
slug: Web/JavaScript/Reference/Global_Objects/Math/abs
translation_of: Web/JavaScript/Reference/Global_Objects/Math/abs
---
<div>{{JSRef("Global_Objects", "Math")}}</div>
<p><code><strong>Math.abs(x)</strong></code> 函数返回指定数字 “x“ 的绝对值。如下：</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><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>
<h2 id="Syntax" name="Syntax">语法</h2>
<pre class="syntaxbox">Math.abs(<em>x</em>);</pre>
<h3 id="Parameters" name="Parameters">参数</h3>
<dl>
<dt><code>x</code></dt>
<dd>一个数值</dd>
</dl>
<h2 id="Description" name="Description">说明</h2>
<p><code><font face="Open Sans, sans-serif">由于 </font>Math.abs()</code> <code>是</code> <code>Math</code> 中的一个静态方法，你应该通过 <code>Math.abs()</code> <code>调用。</code>（Math 不是构造器）</p>
<h2 id="Examples" name="Examples">示例</h2>
<h3 id="Example:_Math.abs_behavior" name="Example:_Math.abs_behavior"><code>Math.abs()函数的行为</code></h3>
<p>传入一个非数字形式的字符串或者 undefined/empty 变量，将返回 <code>NaN</code>。传入 null 将返回 0。</p>
<pre class="brush:js">Math.abs('-1'); // 1
Math.abs(-2); // 2
Math.abs(null); // 0
Math.abs("string"); // NaN
Math.abs(); // NaN</pre>
<h2 id="规范">规范</h2>
<table class="standard-table">
<tbody>
<tr>
<th scope="col">规范版本</th>
<th scope="col">规范状态</th>
<th scope="col">注解</th>
</tr>
<tr>
<td>ECMAScript 1st Edition. Implemented in JavaScript 1.0</td>
<td>Standard</td>
<td>Initial definition.</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>
</tbody>
</table>
<h2 id="浏览器兼容性">浏览器兼容性</h2>
<p>{{ CompatibilityTable() }}</p>
<div id="compat-desktop">
<table class="compat-table">
<tbody>
<tr>
<th>Feature</th>
<th>Chrome</th>
<th>Firefox (Gecko)</th>
<th>Internet Explorer</th>
<th>Opera</th>
<th>Safari</th>
</tr>
<tr>
<td>Basic support</td>
<td>{{ CompatVersionUnknown() }}</td>
<td>{{ CompatVersionUnknown() }}</td>
<td>{{ CompatVersionUnknown() }}</td>
<td>{{ CompatVersionUnknown() }}</td>
<td>{{ CompatVersionUnknown() }}</td>
</tr>
</tbody>
</table>
</div>
<div id="compat-mobile">
<table class="compat-table">
<tbody>
<tr>
<th>Feature</th>
<th>Android</th>
<th>Chrome for Android</th>
<th>Firefox Mobile (Gecko)</th>
<th>IE Mobile</th>
<th>Opera Mobile</th>
<th>Safari Mobile</th>
</tr>
<tr>
<td>Basic support</td>
<td>{{ CompatVersionUnknown() }}</td>
<td>{{ CompatVersionUnknown() }}</td>
<td>{{ CompatVersionUnknown() }}</td>
<td>{{ CompatVersionUnknown() }}</td>
<td>{{ CompatVersionUnknown() }}</td>
<td>{{ CompatVersionUnknown() }}</td>
</tr>
</tbody>
</table>
</div>
<h2 id="See_also" name="See_also">相关链接</h2>
<ul>
<li>The {{jsxref("Global_Objects/Math", "Math")}} object it belongs to.</li>
<li>{{jsxref("Math.ceil()")}}</li>
<li>{{jsxref("Math.floor()")}}</li>
<li>{{jsxref("Math.round()")}}</li>
</ul>
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