You will need to use Babel or another processor for the newer syntax and features, which will compile you ES5ish JavaScript that browsers will mostly understand

You will need to use Babel or another processor for the newer syntax and features, which will compile you ES5ish JavaScript that browsers will mostly understand. Compiling JavaScript is one solution to the problem that you have no control over the client interpreter and the 'version' of your code that it supports. It isn't an ideal solution, but it means we can move the language forward without worrying about breaking everything.