# Math.asin()

## BaselineWidely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

## 概述

Math.asin() 方法返回一个数值的反正弦（单位为弧度），即：

$∀ x ∊ [ - 1 ; 1 ] , Math.asin ( x ) = arcsin ( x ) = the unique y ∊ [ - π 2 ; π 2 ] such that sin ( y ) = x \forall x \in [{-1};1],;\mathtt{\operatorname{Math.asin}(x)} = \arcsin(x) = \text{ the unique } ; y \in \left[-\frac{\pi}{2}; \frac{\pi}{2}\right] , \text{such that} ; \sin(y) = x$

## 语法

Math.asin(x)


### 参数

x

## 描述

asin 方法接受 -1 到 1 之间的数值作为参数，返回一个介于 $-\frac\left\{\pi\right\}\left\{2\right\}$$\frac\left\{\pi\right\}\left\{2\right\}$ 弧度的数值。如果接受的参数值超出范围，则返回 NaN

## 示例

### 示例：使用 Math.asin()

js
Math.asin(-2); // NaN
Math.asin(-1); // -1.5707963267948966 (-pi/2)
Math.asin(0); // 0
Math.asin(0.5); // 0.5235987755982989
Math.asin(1); // 1.5707963267948966 (pi/2)
Math.asin(2); // NaN


## 规范

Specification
ECMAScript Language Specification
# sec-math.asin

## 浏览器兼容性

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