pad.js

/**
 * Pad a number, in string format, with leading zeros.
 * @param {number|string} num The number to pad
 * @param {number} [size] The target length
 * @returns {string} The padded number.
 */
function pad(num, size) {
    size = size || 2;
	var s = num + "";
    while (s.length < size) s = "0" + s;
    return s;
}