Math.log2()
The Math.log2()
function returns the base 2 logarithm of a number, that is
Syntax
Math.log2(<var>x</var>)
Parameters
x
- A number.
Return value
The base 2 logarithm of the given number. If the number is negative, NaN
is returned.
Description
If the value of x
is less than 0, the return value is always NaN
.
Because log2()
is a static method of Math
, you always use it as Math.log2()
, rather than as a method of a Math
object you created (Math
is not a constructor).
This function is the equvalent of Math.log(x) / Math.log(2). For log2(e) use the constant Math.LOG2E
which is 1 / Math.LN2
.
Examples
Using Math.log2()
Math.log2(3); // 1.584962500721156 Math.log2(2); // 1 Math.log2(1); // 0 Math.log2(0); // -Infinity Math.log2(-2); // NaN Math.log2(1024); // 10
Polyfill
This Polyfill emulates the Math.log2
function. Note that it returns imprecise values on some inputs (like 1 << 29), wrap into Math.round()
if working with bit masks.
Math.log2 = Math.log2 || function(x) { return Math.log(x) * Math.LOG2E; };
Specifications
Specification | Status | Comment |
---|---|---|
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'Math.log2' in that specification. |
Standard | Initial definition. |
ECMAScript 2017 Draft (ECMA-262) The definition of 'Math.log2' in that specification. |
Draft |
Browser compatibility
Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|
Basic support | 38 | 25 (25) | No support | 25 | 7.1 |
Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|---|
Basic support | No support | No support | 25.0 (25) | No support | No support | 8 |
See also
License
© 2016 Mozilla Contributors
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-us/docs/web/javascript/reference/global_objects/math/log2