---
title: Math.expm1()
slug: Web/JavaScript/Reference/Global_Objects/Math/expm1
translation_of: Web/JavaScript/Reference/Global_Objects/Math/expm1
---
<div>{{JSRef("Global_Objects", "Math")}}</div>

<h2 id="Summary">概述</h2>

<p><code><strong>Math.expm1()</strong></code> 函数返回 <code>E^x - 1</code>, 其中 <code>x</code> 是该函数的参数, <code>E</code> 是自然对数的底数 <code>2.718281828459045.</code></p>

<h2 id="Syntax">语法</h2>

<pre class="syntaxbox"><code>Math.expm1(<em>x</em>)</code></pre>

<h3 id="Parameters">参数</h3>

<dl>
 <dt><code>x</code></dt>
 <dd>任意数字.</dd>
</dl>

<h2 id="Description">描述</h2>

<p><code>参数 <code>x</code> 会被自动类型转换成 <code>number </code>类型.</code></p>

<p><code>expm1 是 "exponent minus 1" 的缩写.</code></p>

<h2 id="Examples">示例</h2>

<pre class="brush:js">Math.expm1(1)     // 1.7182818284590453
Math.expm1(-38)   // -1
Math.expm1("-38") // -1
Math.expm1("foo") // NaN
</pre>

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

<p>因为我们已经有了 <code>Math.exp </code>函数, 所以很容易 polyfill.</p>

<pre class="brush: js">Math.expm1 = Math.expm1 || function (x) {
    return Math.exp(x) - 1
}
</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-math.expm1', 'Math.expm1')}}</td>
   <td>{{Spec2('ES6')}}</td>
   <td>Initial definition.</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>{{jsxref("Global_Objects/Math", "Math")}} 对象.</li>
</ul>