Math.asin()

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

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

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 - π 2 -\frac{\pi}{2} and π 2 \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
ECMAScript Language Specification (ECMAScript)
# sec-math.asin

Browser compatibility

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See also