How to output integers with leading zeros in JavaScript

2 Answers

You could extend the Number object:

Number.prototype.pad = function(size) {
    var s = String(this);
    while (s.length < (size || 2)) {s = "0" + s;}
    return s;


(9).pad();  //returns "09"

(7).pad(3);  //returns "007"

Possible Duplicate:
How can I create a Zerofilled value using JavaScript?

I can round to x amount of decimal places with math.round but is there a way to round left of the decimal? for example 5 becomes 05 if I specify 2 places

Just for fun (I had some time to kill), a more sophisticated implementation which caches the zero-string:

pad.zeros = new Array(5).join('0');
function pad(num, len) {
    var str = String(num),
        diff = len - str.length;
    if(diff <= 0) return str;
    if(diff > pad.zeros.length)
        pad.zeros = new Array(diff + 1).join('0');
    return pad.zeros.substr(0, diff) + str;

If the padding count is large and the function is called often enough, it actually outperforms the other methods...


function pad(a,b){return(1e15+a+"").slice(-b)}

With comments:

function pad(
  a, // the number to convert 
  b // number of resulting characters
  return (
    1e15 + a + // combine with large number
    "" // convert to string
  ).slice(-b) // cut leading "1"