JSFiddle - React, Tailwind, and code Playground

JavaScript

// parse dates from DD/MM/YYYY to YYYY/MM/DD
var oldBegin = parseDate("03/06/2012");
var oldEnd = parseDate("07/06/2012");

// calculate difference and fomat to days
var diff = Math.round((oldEnd - oldBegin)/1000/60/60/24);
alert(diff);


function parseDate(str) {
  var m = str.match(/^(\d{1,2})\/(\d{1,2})\/(\d{4})$/);
  return (m) ? new Date(m[3], m[2]-1, m[1]) : null;
}