---
title: Math.atan()
slug: Web/JavaScript/Reference/Global_Objects/Math/atan
translation_of: Web/JavaScript/Reference/Global_Objects/Math/atan
---
<div>
 {{JSRef("Global_Objects", "Math")}}</div>
<h2 id="Summary">概述</h2>
<p><code><strong>Math.atan()</strong></code> 函数返回一个数值的反正切（以弧度为单位），即：</p>
<p><math display="block"><semantics><mrow><mstyle mathvariant="monospace"><mrow><mo lspace="0em" rspace="thinmathspace">Math.atan</mo><mo stretchy="false">(</mo><mi>x</mi><mo stretchy="false">)</mo></mrow></mstyle><mo>=</mo><mo lspace="0em" rspace="0em">arctan</mo><mo stretchy="false">(</mo><mi>x</mi><mo stretchy="false">)</mo><mo>=</mo><mtext> the unique </mtext><mspace width="thickmathspace"></mspace><mi>y</mi><mo>∊</mo><mrow><mo>[</mo><mrow><mo>-</mo><mfrac><mi>π</mi><mn>2</mn></mfrac><mo>;</mo><mfrac><mi>π</mi><mn>2</mn></mfrac></mrow><mo>]</mo></mrow><mspace width="thinmathspace"></mspace><mtext>such that</mtext><mspace width="thickmathspace"></mspace><mo lspace="0em" rspace="0em">tan</mo><mo stretchy="false">(</mo><mi>y</mi><mo stretchy="false">)</mo><mo>=</mo><mi>x</mi></mrow><annotation encoding="TeX">\mathtt{\operatorname{Math.atan}(x)} = \arctan(x) = \text{ the unique } \; y \in \left[-\frac{\pi}{2}; \frac{\pi}{2}\right] \, \text{such that} \; \tan(y) = x</annotation></semantics></math></p>
<h2 id="Syntax">语法</h2>
<pre class="syntaxbox">Math.atan(<em>x</em>)</pre>
<h3 id="Parameters">参数</h3>
<dl>
 <dt>
  <code>x</code></dt>
 <dd>
  一个数值</dd>
</dl>
<h2 id="Description">描述</h2>
<p><code>atan</code> 返回一个 <math><semantics><mrow><mo>-</mo><mfrac><mi>π</mi><mn>2</mn></mfrac></mrow><annotation encoding="TeX">-\frac{\pi}{2}</annotation></semantics></math> 到 <math><semantics><mfrac><mi>π</mi><mn>2</mn></mfrac><annotation encoding="TeX">\frac{\pi}{2}</annotation></semantics></math> 弧度之间的数值。</p>
<p>由于 <code>atan</code> 是 <code>Math</code> 的静态方法，所以应该像这样使用：<code>Math.atan()</code>，而不是作为你创建的 <code>Math</code> 实例的方法。</p>
<h2 id="Examples">示例</h2>
<h3 id="Example:_Using_Math.atan">例子：使用 <code>Math.atan</code></h3>
<pre class="brush:js">Math.atan(1);  // 0.7853981633974483
Math.atan(0);  // 0
</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-15.8.2.4', 'Math.atan')}}</td>
   <td>{{Spec2('ES5.1')}}</td>
   <td> </td>
  </tr>
  <tr>
   <td>{{SpecName('ES6', '#sec-math.atan', 'Math.atan')}}</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>

{{Compat}}

<h2 id="See_also">相关链接</h2>
<ul>
 <li>The {{jsxref("Global_Objects/Math", "Math")}} object it belongs to.</li>
 <li>{{jsxref("Math.acos()")}}</li>
 <li>{{jsxref("Math.asin()")}}</li>
 <li>{{jsxref("Math.atan2()")}}</li>
 <li>{{jsxref("Math.cos()")}}</li>
 <li>{{jsxref("Math.sin()")}}</li>
 <li>{{jsxref("Math.tan()")}}</li>
</ul>