Math.log()

Summary

The Math.log() function returns the natural logarithm (base E) of a number.

Syntax

Math.log(x)

Parameters

x

A number.

Description

If the value of number 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.

Examples

Example: Using Math.log

The following function returns the natural log of the variable x:

function getLog(x) {
   return Math.log(x)
}

If you pass getLog the value 10, it returns 2.302585092994046; if you pass it the value 0, it returns -Infinity; if you pass it the value -1, it returns NaN because -1 is out of range.

Example: Using Math.log with a different base

The following function returns the logarithm of y with base x (ie. log_x y):

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

Browser compatibility

See also

• The Math object it belongs to.
• Math.exp()
• Math.pow()