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+---
+title: Math.tanh()
+slug: Web/JavaScript/Reference/Global_Objects/Math/tanh
+tags:
+  - ECMAScript6
+  - JavaScript
+  - Math
+  - Method
+  - tanh
+  - 双曲正切
+translation_of: Web/JavaScript/Reference/Global_Objects/Math/tanh
+---
+<div>{{JSRef}}</div>
+
+<p><strong><code>Math.tanh()</code></strong> 函数将会返回一个数的双曲正切函数值，公式如下：</p>
+
+<p><math display="block"><semantics><mrow><mo lspace="0em" rspace="0em">tanh</mo><mi>x</mi><mo>=</mo><mfrac><mrow><mo lspace="0em" rspace="0em">sinh</mo><mi>x</mi></mrow><mrow><mo lspace="0em" rspace="0em">cosh</mo><mi>x</mi></mrow></mfrac><mo>=</mo><mfrac><mrow><msup><mi>e</mi><mi>x</mi></msup><mo>-</mo><msup><mi>e</mi><mrow><mo>-</mo><mi>x</mi></mrow></msup></mrow><mrow><msup><mi>e</mi><mi>x</mi></msup><mo>+</mo><msup><mi>e</mi><mrow><mo>-</mo><mi>x</mi></mrow></msup></mrow></mfrac><mo>=</mo><mfrac><mrow><msup><mi>e</mi><mrow><mn>2</mn><mi>x</mi></mrow></msup><mo>-</mo><mn>1</mn></mrow><mrow><msup><mi>e</mi><mrow><mn>2</mn><mi>x</mi></mrow></msup><mo>+</mo><mn>1</mn></mrow></mfrac></mrow><annotation encoding="TeX">\tanh x = \frac{\sinh x}{\cosh x} = \frac {e^x - e^{-x}} {e^x + e^{-x}} = \frac{e^{2x} - 1}{e^{2x}+1}</annotation></semantics></math></p>
+
+<div>{{EmbedInteractiveExample("pages/js/math-tanh.html")}}</div>
+
+<h2 id="语法">语法</h2>
+
+<pre class="syntaxbox"><code>Math.tanh(<var>x</var>)</code></pre>
+
+<h3 id="参数">参数</h3>
+
+<dl>
+ <dt><code>x</code></dt>
+ <dd>待计算的数字。</dd>
+</dl>
+
+<h3 id="返回值">返回值</h3>
+
+<p>所给数字的双曲正切值。</p>
+
+<h2 id="描述">描述</h2>
+
+<p>因为 <code>tanh()</code> 是 <code>Math</code> 的静态方法，所以总应该直接调用 <code>Math.tanh()</code> ，而不是创建 <code>Math</code> 对象再调用该方法（<code>Math</code> 不是一个构造函数）。</p>
+
+<h2 id="示例">示例</h2>
+
+<h3 id="使用_Math.tanh">使用 <code>Math.tanh()</code></h3>
+
+<pre class="brush: js">Math.tanh(0);        // 0
+Math.tanh(Infinity); // 1
+Math.tanh(1);        // 0.7615941559557649
+</pre>
+
+<h2 id="向下兼容">向下兼容</h2>
+
+<p><code>tanh()</code> 可以通过 {{jsxref("Math.exp()")}} 函数实现：</p>
+
+<pre class="brush: js">Math.tanh = Math.tanh || function(x){
+    var a = Math.exp(+x), b = Math.exp(-x);
+    return a == Infinity ? 1 : b == Infinity ? -1 : (a - b) / (a + b);
+}</pre>
+
+<h2 id="规范">规范</h2>
+
+<table class="standard-table">
+ <tbody>
+  <tr>
+   <th scope="col">规范</th>
+  </tr>
+  <tr>
+   <td>{{SpecName('ESDraft', '#sec-math.tanh', 'Math.tanh')}}</td>
+  </tr>
+ </tbody>
+</table>
+
+<h2 id="浏览器兼容性">浏览器兼容性</h2>
+
+<p class="hidden">The compatibility table in this page is generated from structured data. If you'd like to contribute to the data, please check out <a href="https://github.com/mdn/browser-compat-data">https://github.com/mdn/browser-compat-data</a> and send us a pull request.</p>
+
+<p>{{Compat("javascript.builtins.Math.tanh")}}</p>
+
+<h2 id="参见">参见</h2>
+
+<ul>
+ <li>{{jsxref("Math.acosh()")}}</li>
+ <li>{{jsxref("Math.asinh()")}}</li>
+ <li>{{jsxref("Math.atanh()")}}</li>
+ <li>{{jsxref("Math.cosh()")}}</li>
+ <li>{{jsxref("Math.sinh()")}}</li>
+</ul>