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('/');
}