Math.log2()

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

x>0,Math.log2(x)=log2(x)=the uniqueysuch that2y=x\forall x > 0, \mathtt{\operatorname{Math.log2}(x)} = \log_2(x) = \text{the unique} \; y \; \text{such that} \; 2^y = x

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.  

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 Latest Draft (ECMA-262)
The definition of 'Math.log2' in that specification.
Draft  

Browser compatibility

FeatureChromeFirefoxEdgeInternet ExplorerOperaSafari
Basic Support3825(Yes)(No)257.1
FeatureAndroidChrome for AndroidEdge mobileFirefox for AndroidIE mobileOpera AndroidiOS Safari
Basic Support(Yes)(Yes)(Yes)25(No)(Yes)8

See also

Document Tags and Contributors

 Last updated by: fscholz,