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---
title: Math.PI
slug: Web/JavaScript/Reference/Global_Objects/Math/PI
translation_of: Web/JavaScript/Reference/Global_Objects/Math/PI
---
<div>{{JSRef("Global_Objects", "Math")}}</div>
<h2 id="Summary" name="Summary">概述</h2>
<p><code><strong>Math.PI</strong></code> 表示一个圆的周长与直径的比例，约为 3.14159：</p>
<p><math><semantics><mrow><mstyle mathvariant="monospace"><mi>Math.PI</mi></mstyle><mo>=</mo><mi>π</mi><mo>≈</mo><mn>3.14159</mn></mrow><annotation encoding="TeX">\mathtt{\mi{Math.PI}} = \pi \approx 3.14159</annotation></semantics></math></p>
<div>{{js_property_attributes(0,0,0)}}</div>
<h2 id="Description" name="Description">描述</h2>
<p>由于 <code>PI</code> 是 <code>Math</code> 的静态属性，所以应该像这样使用：<code>Math.PI</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" name="Examples">示例</h2>
<h3 id="Example:_Using_PI" name="Example:_Using_PI">使用 <code>Math.PI</code></h3>
<p>下面的函数使用 Math.PI 计算给定半径的圆周长：</p>
<pre class="brush:js language-js" style="padding: 1em 0px 1em 30px; font-size: 14px; white-space: normal; color: rgb(77, 78, 83);"><code class="language-js" style="direction: ltr; white-space: pre;">function calculateCircumference (radius) {
return 2 * Math.PI * radius;
}
calculateCircumference(1); // 6.283185307179586</code></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-15.8.1.6', 'Math.PI')}}</td>
<td>{{Spec2('ES5.1')}}</td>
<td> </td>
</tr>
<tr>
<td>{{SpecName('ES6', '#sec-math.pi', 'Math.PI')}}</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>
</ul>
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