How can I count the number of zero decimals in JavaScript?

Question

How do I get the number of zero decimals behind the comma (but not the total)? So to illustrate an example:

0.00001 > 4
0.000015 > 4
0.0000105 > 4
0.001 > 2

I am looking for methods that are efficient (meaning that they optimize the calculation time).

Answer 1

You can use logarithms to find the magnitude of the number:

var x = 0.00195;
var m = -Math.floor( Math.log(x) / Math.log(10) + 1);
document.write(m); // outputs 2

Later versions of JavaScript have Math.log10, so it would be:

var x = 0.00195;
var m = -Math.floor( Math.log10(x) + 1);
document.write(m); // outputs 2

How using the base-10 logarithm of the numbers works:

x	Math.log10(x)	Math.floor(Math.log10(x) + 1 )
0.1	-1	0
0.01	-2	-1
0.015	-1.8239…	-1
0.001	-3	-2
0.00001	-5	-4
0.000015	-4.8239…	-4
0.0000105	-4.9788…	-4

Answer 2

Use a regex to match the number of zeros after a decimal point and then count them.

var zeros = float.toString().match(/(\.0*)/)[0].length - 1;

DEMO