# Math.atanh()

Math.atanh() 函数返回一个数值反双曲正切值, 即：

$∀x∊(-1,1),Math.atanh(x)=arctanh(x)= the unique ysuch thattanh(y)=x\forall x \in \left( -1, 1 \right), \mathtt{\operatorname{Math.atanh}(x)} = \operatorname{arctanh}(x) = \text{ the unique } \; y \; \text{such that} \; \tanh(y) = x$

## 语法

Math.atanh(x)

### 参数

x

## 示例

### 使用 Math.atanh()

Math.atanh(-2);  // NaN
Math.atanh(-1);  // -Infinity
Math.atanh(0);   // 0
Math.atanh(0.5); // 0.5493061443340548
Math.atanh(1);   // Infinity
Math.atanh(2);   // NaN


## Polyfill

For \left|x\right| < 1, we have \operatorname {artanh} (x) = \frac{1}{2}\ln \left( \frac{1 + x}{1 - x} \right) so this can be emulated by the following function:

Math.atanh = Math.atanh || function(x) {
return Math.log((1+x)/(1-x)) / 2;
};


## 规范

Specification Status Comment
ECMAScript 2015 (6th Edition, ECMA-262)
Math.atanh
Standard Initial definition.
ECMAScript Latest Draft (ECMA-262)
Math.atanh
Draft

## 浏览器兼容性

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Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support 38 25 (25) 未实现 25 7.1
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