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?
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8There is a Math.log10() method ever since ECMAScript 2015 for those who come here later on.– HaggraCommented Dec 10, 2019 at 20:19
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10 Answers
"Change of Base" Formula / Identity
The numerical value for logarithm to the base 10 can be calculated with the following identity.
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);
}
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11In fact, any base can be used, not just e or 2, as long as both logarithms use the same base.– JoeyCommented Jun 10, 2010 at 23:40
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16Added an image with the formula and linked to Wikipedia if you don't mind.– AnuragCommented Jun 10, 2010 at 23:40
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16Wasteful to calculate Math.log(10) each time. Unnecessary to precalculate and store since Math defines this constant already w3schools.com/jsref/jsref_ln10.asp Commented Jun 27, 2012 at 8:43
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6For bases other than 10, scroll down to CMS's answer. If scrolling down and reading an answer sounds like hard work, basic principle is
return Math.log(n) / Math.log(base);Commented Jan 22, 2013 at 11:55 -
4I've noticed some potential room for error here, probably having to do with floating point math. I just tried the function above with a value of 1000 in node, and got a result of 2.9999999999999996. (Although other numbers I tried, such as 10, 100, and even 10000, came out with correct values.) Commented Apr 13, 2013 at 14:44
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);
answered Jun 10, 2010 at 23:38
const logBase = (n, base) => Math.log(n) / Math.log(base);
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
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14Adjust precision with selective rounding:
(Math.round(Math.log(1000) / Math.LN10 * 1e6) / 1e6)Commented Nov 21, 2013 at 5:01
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 7.1Mobile 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
answered Aug 1, 2014 at 10:48
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
answered May 19, 2020 at 17:23
