function padLeadingZeros(num, size) { var s = num+""; while (s.length < size) s = "0" + s; return s; } padLeadingZeros(57, 3);// "057" padLeadingZeros(57, 4); //"0057"
String(<number>).padStart(<places>, '0') String(42).padStart(5, '0'); // '00042'