Pad Number with Leading Zero in Javascript

The following function will pad number with leading zero(es).

function pad(number, length) {
   var str = '' + number;
   while (str.length < length) {
   str = '0' + str;
   }
   return str;
} 

Some code to test the function:

document.write(pad(1, 1) + '');
document.write(pad(1, 2) + '');
document.write(pad(15, 2) + '');
document.write(pad(1, 3) + '');
document.write(pad(15, 3) + '');
document.write(pad(155, 3) + '');
document.write(pad(1, 4) + '');
document.write(pad(1, 5) + ''); 

And the result output:

1

01
15
001
015
155
0001
00001

http://www.electrictoolbox.com/pad-number-zeroes-javascript/