Javascript change date into format of (dd/mm/yyyy)

Some JavaScript engines can parse that format directly, which makes the task pretty easy:

function convertDate(inputFormat) {
  function pad(s) { return (s < 10) ? '0' + s : s; }
  var d = new Date(inputFormat)
  return [pad(d.getDate()), pad(d.getMonth()+1), d.getFullYear()].join('/')
}

console.log(convertDate('Mon Nov 19 13:29:40 2012')) // => "19/11/2012"

This will ensure you get a two-digit day and month.

function formattedDate(d = new Date) {
  let month = String(d.getMonth() + 1);
  let day = String(d.getDate());
  const year = String(d.getFullYear());

  if (month.length < 2) month = '0' + month;
  if (day.length < 2) day = '0' + day;

  return `${day}/${month}/${year}`;
}

Or terser:

function formattedDate(d = new Date) {
  return [d.getDate(), d.getMonth()+1, d.getFullYear()]
      .map(n => n < 10 ? `0${n}` : `${n}`).join('/');
}