JSFiddle - React, Tailwind, and code Playground

by Kyros Koh

HTML

<div id = "result"/>

JavaScript

String.prototype.insert = function (index, string) {
  if (index > 0)
    return this.substring(0, index) + string + this.substring(index, this.length);
  else
    return string + this;
};

var data = "123";
if (data.length == 3) {
data = data.insert(0, "0");
data = data.insert(2, ":");
var data2 = data2.insert(5, ":");
data2 = data2.insert(6, ":00");
}
else if (data.length == 4) {
data = data.insert(2, ":");
var data2 = data2.insert(5, ":");
data2 = data2.insert(6, ":00");
}    
else { data2 = "Error"; }

document.getElementById("result").innerHTML = data2;