---
title: Math.SQRT1_2
slug: Web/JavaScript/Reference/Global_Objects/Math/SQRT1_2
translation_of: Web/JavaScript/Reference/Global_Objects/Math/SQRT1_2
---
<div>
 {{JSRef("Global_Objects", "Math")}}</div>
<h2 id="Summary">概述</h2>
<p><code><strong>Math.SQRT1_2</strong></code> 属性表示 1/2 的平方根，约为 0.707：</p>
<p><math display="block"><semantics><mrow><mstyle mathvariant="monospace"><mi>Math.SQRT1_2</mi></mstyle><mo>=</mo><msqrt><mfrac><mn>1</mn><mn>2</mn></mfrac></msqrt><mo>=</mo><mfrac><mn>1</mn><msqrt><mn>2</mn></msqrt></mfrac><mo>≈</mo><mn>0.707</mn></mrow><annotation encoding="TeX">\mathtt{\mi{Math.SQRT1_2}} = \sqrt{\frac{1}{2}} = \frac{1}{\sqrt{2}} \approx 0.707</annotation></semantics></math></p>
<div>
 {{js_property_attributes(0,0,0)}}</div>
<h2 id="Description">描述</h2>
<p>由于 <code>SQRT1_2</code> 是 <code>Math</code> 对象的静态属性，所以应该像这样使用：<code>Math.SQRT1_2</code>，而不是作为你创建的 <code>Math</code> 实例的属性（<code>Math</code> 不是构造函数）。</p>
<h2 id="Examples">示例</h2>
<h3 id="Example:_Using_SQRT1_2">例子：使用 <code>SQRT1_2</code></h3>
<p>下面的函数返回 1/2 的平方根：</p>
<pre class="brush:js">function getRoot1_2() {
   return Math.SQRT1_2
}

getRoot1_2() // 0.7071067811865476</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-15.8.1.7', 'Math.SQRT1_2')}}</td>
   <td>{{Spec2('ES5.1')}}</td>
   <td> </td>
  </tr>
  <tr>
   <td>{{SpecName('ES6', '#sec-math.sqrt1_2', 'Math.SQRT1_2')}}</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>
</ul>