Web/JavaScript/Reference/Global objects/Math/log2

The Math.log2() function returns the base 2 logarithm of a number, that is

<math display="block">\forall x > 0,\mathtt{\operatorname{Math.log2}(x)} = \log_{2}(x) = \text{the\ unique}\; y\;\text{such\ that}\; 2^{y} = x</math>

Syntax

Math.log2(x)

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 equivalent of Math.log(x) / Math.log(2). For log2(e) use the constant Math.LOG2E which is 1 / Math.LN2.

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.

if (!Math.log2) Math.log2 = function(x) {
  return Math.log(x) * Math.LOG2E;
};

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

Specifications

Specification
ECMAScript (ECMA-262)The definition of 'Math.log2' in that specification.

Browser compatibility

Update compatibility data on GitHub

	Desktop						Mobile						Server
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet	Node.js
`log2`	Chrome Full support 38	Edge Full support 12	Firefox Full support 25	IE No support No	Opera Full support 25	Safari Full support 8	WebView Android Full support 38	Chrome Android Full support 38	Firefox Android Full support 25	Opera Android Full support 25	Safari iOS Full support 8	Samsung Internet Android Full support 3.0	nodejs Full support 0.12

Legend

Full support: Full support
No support: No support