Math.asin

The Math.asin() function returns the arcsine (in radians) of a number, that is

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

Syntax

Math.asin(x)

Parameters

x

A number.

Return value

The arcsine (in radians) of the given number if it's between -1 and 1; otherwise, NaN.

Description

The Math.asin() method returns a numeric value between $-\frac{\pi}{2}$ and $\frac{\pi}{2}$ radians for x between -1 and 1. If the value of x is outside this range, it returns NaN.

Because asin() is a static method of Math, you always use it as Math.asin(), rather than as a method of a Math object you created (Math is not a constructor).

Examples

Using Math.asin()

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

For values less than -1 or greater than 1, Math.asin() returns NaN.

Specifications

Specification	Status	Comment
ECMAScript 1st Edition (ECMA-262)	Standard	Initial definition. Implemented in JavaScript 1.0.
ECMAScript 5.1 (ECMA-262) The definition of 'Math.asin' in that specification.	Standard
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'Math.asin' in that specification.	Standard
ECMAScript 2017 Draft (ECMA-262) The definition of 'Math.asin' in that specification.	Draft

Browser compatibility

See also

• Math.acos()
• Math.atan()
• Math.atan2()
• Math.cos()
• Math.sin()
• Math.tan()