add leading zero of 0-9 in javascript code example

Example 1: js number add zero before

('0' + 11).slice(-2) // '11'
('0' + 4).slice(-2)  // '04'

Example 2: javascript print int with leading zeros

function padLeadingZeros(num, size) {
    var s = num+"";
    while (s.length < size) s = "0" + s;
    return s;
}
padLeadingZeros(57, 3);// "057"
padLeadingZeros(57, 4); //"0057"