add leading zeros 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"

Example 3: js num to string with leading 0

String(<number>).padStart(<places>, '0')

String(42).padStart(5, '0'); 	// '00042'