Math.acos()
Baseline
Widely available
This feature is well established and works across many devices and browser versions. Itās been available across browsers since āØJuly 2015ā©.
The Math.acos() static method returns the inverse cosine (in radians) of a number. That is,
Try it
// Calculates angle of a right-angle triangle in radians
function calcAngle(adjacent, hypotenuse) {
return Math.acos(adjacent / hypotenuse);
}
console.log(calcAngle(8, 10));
// Expected output: 0.6435011087932843
console.log(calcAngle(5, 3));
// Expected output: NaN
Syntax
js
Math.acos(x)
Parameters
x-
A number between -1 and 1, inclusive, representing the angle's cosine value.
Return value
The inverse cosine (angle in radians between 0 and Ļ, inclusive) of x. If x is less than -1 or greater than 1, returns NaN.
Description
Because acos() is a static method of Math, you always use it as Math.acos(), rather than as a method of a Math object you created (Math is not a constructor).
Examples
Using Math.acos()
js
Math.acos(-2); // NaN
Math.acos(-1); // 3.141592653589793 (Ļ)
Math.acos(0); // 1.5707963267948966 (Ļ/2)
Math.acos(0.5); // 1.0471975511965979 (Ļ/3)
Math.acos(1); // 0
Math.acos(2); // NaN
Specifications
| Specification |
|---|
| ECMAScriptĀ® 2026 LanguageĀ Specification # sec-math.acos |