string_padding.js

function pad (n, width, z) {
    z = z || '0';
    n = n + '';
    while (n.length < width) { n = z + n; }
    return n;
}

string_padding_verbose.js

function padString (str, width, paddingStr) {
    paddingStr = paddingStr || '0';
    str = str + '';
    while (str.length < width) { str = paddingStr + str; }
    return str;
}