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The Math.log()
function returns the natural logarithm (base e
) of a number, that is
Syntax
Math.log(x)
Parameters
x
- A number.
Return value
The natural logarithm (base e
) of the given number. If the number is negative, NaN
is returned.
Description
If the value of x
is negative, the return value is always NaN
.
Because log()
is a static method of Math
, you always use it as Math.log()
, rather than as a method of a Math
object you created (Math
is not a constructor).
If you need the natural log of 2 or 10, use the constants Math.LN2
or Math.LN10
. If you need a logarithm to base 2 or 10, use Math.log2()
or Math.log10()
. If you need a logarithm to other bases, use Math.log(x) / Math.log(otherBase) as in the example below; you might want to precalculate 1 / Math.log(otherBase) .
Examples
Using Math.log()
Math.log(-1); // NaN, out of range Math.log(0); // -Infinity Math.log(1); // 0 Math.log(10); // 2.302585092994046
Using Math.log()
with a different base
The following function returns the logarithm of y
with base x
(ie. ):
function getBaseLog(x, y) { return Math.log(y) / Math.log(x); }
If you run getBaseLog(10, 1000)
it returns 2.9999999999999996
due to floating-point rounding, which is very close to the actual answer of 3.
Specifications
Specification | Status | Comment |
---|---|---|
ECMAScript 1st Edition (ECMA-262) | Standard | Initial definition. Implemented in JavaScript 1.0. |
ECMAScript 5.1 (ECMA-262) The definition of 'Math.log' in that specification. |
Standard | |
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'Math.log' in that specification. |
Standard | |
ECMAScript 2017 Draft (ECMA-262) The definition of 'Math.log' in that specification. |
Draft |
Browser compatibility
Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|
Basic support | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|---|
Basic support | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |