TheMath.log() static method returns the natural logarithm (basee) of a number. That is

Try it

function getBaseLog(x, y) {  return Math.log(y) / Math.log(x);}// 2 x 2 x 2 = 8console.log(getBaseLog(2, 8));// Expected output: 3// 5 x 5 x 5 x 5 = 625console.log(getBaseLog(5, 625));// Expected output: 4

Syntax

Math.log(x)

Parameters

x

A number greater than or equal to 0.

Return value

The natural logarithm (basee) ofx. Ifx is ±0, returns-Infinity. Ifx < 0, returnsNaN.

Description

Becauselog() is a static method ofMath, you always use it asMath.log(), rather than as a method of aMath object you created (Math is not a constructor).

If you need the natural log of 2 or 10, use the constantsMath.LN2 orMath.LN10. If you need a logarithm to base 2 or 10, useMath.log2() orMath.log10(). If you need a logarithm to other bases, useMath.log(x) / Math.log(otherBase) as in the example below; you might want to precalculate1 / Math.log(otherBase) since multiplication inMath.log(x) * constant is much faster.

Beware that positive numbers very close to 1 can suffer from loss of precision and make its natural logarithm less accurate. In this case, you may want to useMath.log1p instead.

Examples

Using Math.log()

Math.log(-1); // NaNMath.log(-0); // -InfinityMath.log(0); // -InfinityMath.log(1); // 0Math.log(10); // 2.302585092994046Math.log(Infinity); // Infinity

Using Math.log() with a different base

The following function returns the logarithm ofy with basex (i.e.,${log}_{x}y$):

function getBaseLog(x, y) {  return Math.log(y) / Math.log(x);}

If you rungetBaseLog(10, 1000), it returns2.9999999999999996 due to floating-point rounding, but still very close to the actual answer of 3.

Specifications

Browser compatibility

See also

• Math.exp()
• Math.log1p()
• Math.log10()
• Math.log2()
• Math.pow()