Easiest way to format dates in Javascript is by far using a modern date / time library. I personally use MomentJS and it works well. I highly recommend this solution if you plan on working with dates in even just a few areas of your app.
Using moment, you could simply call moment(myDate).format("DD/MM/YYYY");.
If you really want to stick to pure Javascript, however, here's how to get the format you want:
const formattedDate = `${myDate.getDate() + 1}/${myDate.getMonth() + 1}/${myDate.getFullYear()}`;
Javascript's built-in date functions are pretty confusing. Here, for instance, the getDate and getMonth methods return the index of the date / month, and not the actual date / month, so we need to add +1 to those.
Using vanilla Javascript then becomes even harder when dealing with date manipulation (adding, subtracting) and timezones.