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    Math.log()

    Summary

    The Math.log() function returns the natural logarithm (base e) of a number, that is

    x>0,Math.log(x)=ln(x)=the uniqueysuch thatey=x\forall x > 0, \mathtt{\operatorname{Math.log}(x)} = \ln(x) = \text{the unique} \; y \; \text{such that} \; e^y = x

    Syntax

    Math.log(x)

    Parameters

    x
    A number.

    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).

    Examples

    Example: Using Math.log()

    Math.log(-1); // NaN, out of range
    Math.log(0);  // -Infinity
    Math.log(1);  // 0
    Math.log(10); // 2.302585092994046
    

    Example: Using Math.log() with a different base

    The following function returns the logarithm of y with base x (ie. logxy\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

    Specification Status Comment
    ECMAScript 1st Edition. 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  

    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)

    See also

    Document Tags and Contributors

    Last updated by: Mingun,