How can I specify the base for Math.log() in JavaScript?

I need a log function for JavaScript, but it needs to be base 10. I can't see any listing for this, so I'm assuming it's not possible. Are there any math wizards out there who know a solution for this?

"Change of Base" Formula / Identity > The numerical value for logarithm to the base 10 can be calculated > with the following identity.

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Since Math.log(x) in JavaScript returns the natural logarithm of x (same as ln(x)), for base 10 you can divide by Math.log(10) (same as ln(10)):

function log10(val) {
  return Math.log(val) / Math.LN10;
}

Math.LN10 is a built-in precomputed constant for Math.log(10), so this function is essentially identical to:

function log10(val) {
  return Math.log(val) / Math.log(10);
}

Easy, just change the base by dividing by the log(10). There is even a constant to help you

Math.log(num) / Math.LN10;

which is the same as:

Math.log(num) / Math.log(10);

You can simply divide the logarithm of your value, and the logarithm of the desired base, also you could override the Math.log method to accept an optional base argument:

Math.log = (function() {
  var log = Math.log;
  return function(n, base) {
    return log(n)/(base ? log(base) : 1);
  };
})();

Math.log(5, 10);

the answer here would cause obvious precision problem and is not reliable in some use cases

> Math.log(10)/Math.LN10
1

> Math.log(100)/Math.LN10
2

> Math.log(1000)/Math.LN10
2.9999999999999996

> Math.log(10000)/Math.LN10
4

const logBase = (n, base) => Math.log(n) / Math.log(base);

https://en.wikipedia.org/wiki/Logarithm#Change_of_base

Math.log10 = function(n) {
    return (Math.log(n)) / (Math.log(10));
}

Then you can do

Math.log10(your_number);

NOTE: Initially I thought to do Math.prototype.log10 = ... to do this, but user CMS pointed out that Math doesn't work this way, so I edited out the .prototype part.

FF 25+ supports a Math.log10 method. You may to use polyfill:

if (!Math.log10) Math.log10 = function(t){ return Math.log(t)/Math.LN10; };

MDN lists the supported browsers.

>###Desktop Browsers

>

> Chrome Firefox (Gecko) Internet Explorer Opera Safari 38 25 (25) Not supported 25 7.1

>###Mobile Browsers

>

> Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile Not supported Not supported 25.0 (25) Not supported Not supported iOS 8

Math.log10(x)! 

The top answer is fine for an arbitrary base, but the question is regarding log base 10, and Math.log10(x) has been standard across all browsers since 2015.*

*Except IE, if that's important to you for some reason.

If you have a number x, then use of Math.log(x) would essentially be lnx.

To convert it to a base other than e, you can use the following function :

function(x){ return Math.log(x)/Math.log(10); }

For base 10 use Math.log10().

See docs at: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/log10