JSFiddle - React, Tailwind, and code Playground

JavaScript

String.prototype.lpad = function(padString, length) {
    var str = this;
    while (str.length < length)
        str = padString + str;
    return str;
}
    
var str = "5";
alert(str.lpad("0", 4)); //result "0005"
var str = "10";
alert(str.lpad("0", 4)); //result "0010"