1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
|
---
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" name="Summary">概述</h2>
<p><code><strong>Math.expm1()</strong></code> 函数返回 <code>E<sup>x</sup> - 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" name="Syntax">语法</h2>
<pre class="syntaxbox"><code>Math.expm1(<em>x</em>)</code></pre>
<h3 id="Parameters" name="Parameters">参数</h3>
<dl>
<dt><code>x</code></dt>
<dd>任意数字.</dd>
</dl>
<h2 id="Description" name="Description">描述</h2>
<p><code><span style="color: #4d4e53; font-family: 'Open Sans',sans-serif; line-height: 21px;">参数 </span><code style="font-size: 14px; line-height: inherit; margin: 0px; padding: 0px; border: 0px; color: rgb(77, 78, 83);">x</code><span style="color: #4d4e53; font-family: 'Open Sans',sans-serif; line-height: 21px;"> 会被自动类型转换成 </span><code style="font-size: 14px; line-height: inherit; margin: 0px; padding: 0px; border: 0px; color: rgb(77, 78, 83);">number </code><span style="color: #4d4e53; font-family: 'Open Sans',sans-serif; line-height: 21px;">类型.</span></code></p>
<p><code>expm1 是 "exponent minus 1" 的缩写.</code></p>
<h2 id="Examples" name="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>
<p>{{ CompatibilityTable() }}</p>
<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>{{CompatNo}}</td>
<td>{{CompatGeckoDesktop("25")}}</td>
<td>{{CompatNo}}</td>
<td>{{CompatNo}}</td>
<td>{{CompatNo}}</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")}}</td>
<td>{{CompatNo}}</td>
<td>{{CompatNo}}</td>
<td>{{CompatNo}}</td>
</tr>
</tbody>
</table>
</div>
<h2 id="See_also" name="See_also">相关链接</h2>
<ul>
<li>{{jsxref("Global_Objects/Math", "Math")}} 对象.</li>
</ul>
|
