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---
title: Math.asin()
slug: Web/JavaScript/Reference/Global_Objects/Math/asin
translation_of: Web/JavaScript/Reference/Global_Objects/Math/asin
---
<div>
{{JSRef("Global_Objects", "Math")}}</div>
<h2 id="Summary">概述</h2>
<p><code><strong>Math.asin()</strong></code> 方法返回一个数值的反正弦（单位为弧度），即：</p>
<p><math display="block"><semantics><mrow><mo>∀</mo><mi>x</mi><mo>∊</mo><mo stretchy="false">[</mo><mrow><mo>-</mo><mn>1</mn></mrow><mo>;</mo><mn>1</mn><mo stretchy="false">]</mo><mo>,</mo><mspace width="thickmathspace"></mspace><mstyle mathvariant="monospace"><mrow><mo lspace="0em" rspace="thinmathspace">Math.asin</mo><mo stretchy="false">(</mo><mi>x</mi><mo stretchy="false">)</mo></mrow></mstyle><mo>=</mo><mo lspace="0em" rspace="0em">arcsin</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">sin</mo><mo stretchy="false">(</mo><mi>y</mi><mo stretchy="false">)</mo><mo>=</mo><mi>x</mi></mrow><annotation encoding="TeX">\forall x \in [{-1};1],\;\mathtt{\operatorname{Math.asin}(x)} = \arcsin(x) = \text{ the unique } \; y \in \left[-\frac{\pi}{2}; \frac{\pi}{2}\right] \, \text{such that} \; \sin(y) = x</annotation></semantics></math></p>
<h2 id="Syntax">语法</h2>
<pre class="syntaxbox">Math.asin(<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>asin</code> 方法接受 -1 到 1 之间的数值作为参数，返回一个介于 <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> 弧度的数值。如果接受的参数值超出范围，则返回 <code>NaN</code>。</p>
<p>由于 <code>asin</code> 是 <code>Math</code> 的静态方法，所有应该像这样使用：<code>Math.asin()</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.asin">例子：使用 <code>Math.asin()</code></h3>
<pre class="brush:js">Math.asin(-2); // NaN
Math.asin(-1); // -1.5707963267948966 (-pi/2)
Math.asin(0); // 0
Math.asin(0.5); // 0.5235987755982989
Math.asin(1); // 1.570796326794897 (pi/2)
Math.asin(2); // NaN</pre>
<p>对于小于 -1 或大于 1 的参数值，<code>Math.asin</code> 返回 <code>NaN</code>。</p>
<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-15.8.2.3', 'Math.asin')}}</td>
<td>{{Spec2('ES5.1')}}</td>
<td> </td>
</tr>
<tr>
<td>{{SpecName('ES6', '#sec-math.asin', 'Math.asin')}}</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.atan()")}}</li>
<li>{{jsxref("Math.atan2()")}}</li>
<li>{{jsxref("Math.cos()")}}</li>
<li>{{jsxref("Math.sin()")}}</li>
<li>{{jsxref("Math.tan()")}}</li>
</ul>
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