Math.log()
The Math.log()
static method returns the natural logarithm (base e) of a number. That is
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Syntax
js
Math.log(x)
Parameters
x
-
A number greater than or equal to 0.
Return value
Description
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)
since multiplication in Math.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 use Math.log1p
instead.
Examples
Using Math.log()
js
Math.log(-1); // NaN
Math.log(-0); // -Infinity
Math.log(0); // -Infinity
Math.log(1); // 0
Math.log(10); // 2.302585092994046
Math.log(Infinity); // Infinity
Using Math.log() with a different base
The following function returns the logarithm of y
with base x
(i.e.
):
js
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, but still very close to the actual answer of 3.
Specifications
Specification |
---|
ECMAScript Language Specification # sec-math.log |
Browser compatibility
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