files/zh-cn/web/javascript/reference/global_objects/number/epsilon/index.html


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---
title: Number.EPSILON
slug: Web/JavaScript/Reference/Global_Objects/Number/EPSILON
translation_of: Web/JavaScript/Reference/Global_Objects/Number/EPSILON
---
<div>{{JSRef}}</div>

<p><strong><code>Number.EPSILON</code></strong> 属性表示 1 与{{jsxref("Number")}}可表示的大于 1 的最小的浮点数之间的差值。</p>

<p>你不必创建一个 {{jsxref("Number")}} 对象来访问这个静态属性（直接使用 <code>Number.EPSILON</code>）。</p>

<div>{{js_property_attributes(0, 0, 0)}}</div>

<h2 id="描述">描述</h2>

<p><code>EPSILON</code> 属性的值接近于 <code>2.2204460492503130808472633361816E-16</code>，或者 <code>2<sup>-52。</sup></code></p>

<h2 id="示例">示例</h2>

<h3 id="测试是否相等">测试是否相等</h3>

<pre class="brush: js">x = 0.2;
y = 0.3;
z = 0.1;
equal = (Math.abs(x - y + z) &lt; Number.EPSILON);
</pre>

<h2 id="Polyfill">Polyfill</h2>

<pre><code>if (Number.EPSILON === undefined) {
    Number.EPSILON = Math.pow(2, -52);
}</code></pre>


<h2 id="规范">规范</h2>

<table class="standard-table">
 <tbody>
  <tr>
   <th scope="col">Specification</th>
   <th scope="col">Status</th>
   <th scope="col">Comment</th>
  </tr>
  <tr>
   <td>{{SpecName('ES6', '#sec-number.epsilon', 'Number.EPSILON')}}</td>
   <td>{{Spec2('ES6')}}</td>
   <td>最初定义</td>
  </tr>
  <tr>
   <td>{{SpecName('ESDraft', '#sec-number.epsilon', 'Number.EPSILON')}}</td>
   <td>{{Spec2('ESDraft')}}</td>
   <td></td>
  </tr>
 </tbody>
</table>

<h2 id="浏览器兼容性">浏览器兼容性</h2>

<div>{{CompatibilityTable}}</div>

<div id="compat-desktop">
<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>{{CompatGeckoDesktop("25.0")}}</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>9</td>
  </tr>
 </tbody>
</table>
</div>

<div id="compat-mobile">
<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>{{CompatNo}}</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatGeckoMobile("25.0")}}</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatNo}}</td>
   <td>9</td>
  </tr>
 </tbody>
</table>
</div>

<h2 id="相关链接">相关链接</h2>

<ul>
 <li>{{jsxref("Number")}}</li>
</ul>