function addLeadingZeros(num : number, len : number) : string {
return String(num).padStart(len, '0');
}
console.log(addLeadingZeros(6, 2));
console.log(addLeadingZeros(2, 3));
console.log(addLeadingZeros(1, 4));
console.log(addLeadingZeros(1000, 3));
/*
run:
"06"
"002"
"0001"
"1000"
*/