Add zeroes to the left of a digit. Useful for date and time applications.

zeropad.js

/*
input = number or numeric string.
length = pad with zeroes until it hits this length.
*/

function zeroPadLeft(input, length){
    var zero = '0', pad = '', len, padded, inp, extract;
    
    /* Convert to string */
    inp = input+'';
    
    arguments[1] ? len = arguments[1] : len = 2;
    
    /* Make a negative value because we want to snip from the end. */
    extract = len; 

    while(len--){
        pad += zero;
    }
        
    padded = pad + input;
    
    return padded.substr(padded.length - extract);
}

Wonky in < IE8. Working on a refinement.

Changed padded.substr(padded.length - extract); so that it works in IE8. Subtracting the length from the padded length so the index returns that number of characters.