How to output numbers with leading zeros in JavaScript? [duplicate]

Question

Is there a way to prepend leading zeros to numbers so that it results in a string of fixed length? For example, 5 becomes "05" if I specify 2 places.

Answer 1

NOTE: Potentially outdated. ECMAScript 2017 includes String.prototype.padStart.

You'll have to convert the number to a string since numbers don't make sense with leading zeros. Something like this:

function pad(num, size) {     num = num.toString();     while (num.length < size) num = "0" + num;     return num; } 

Or, if you know you'd never be using more than X number of zeros, this might be better. This assumes you'd never want more than 10 digits.

function pad(num, size) {     var s = "000000000" + num;     return s.substr(s.length-size); } 

If you care about negative numbers you'll have to strip the - and read it.