Add characters to the beginning of a string if it’s less than a certain length. Accepts two arguments: the length the string should be, and what characters to add if it’s not that length. The characters to use is optional, and defaults to a space ().
// Add a leading zero for hours below 10
var hour3 = '3';
var hour12 = '12';
// returns "03"
hour3.padStart(2, '0');
// returns "12"
hour12.padStart(2, '0');
Source
https://vanillajstoolkit.com/reference/strings/string-padstart/