--- 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>由于 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> <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> <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>