JavaScript » Math » asin

Syntax:
Math.asin(x)

This method returns the arcsine of a number as a numeric value between
-PI/2 and PI/2 radians. Passing it a value for 'x' which is outsite the range -1 to 1 will cause the Netscape browser to return NaN, and the Internet Explorer browser to return an error message. Passing it 1 will return the value of PI/2.