1. Since it sounds that you are more comfortable with pre-ES6 syntax, I would therefore suggest you start coding with pre-ES6 first.
2. Compatibility is not an issue, we can use Babel transpiler for backward compatibility of your ES6 codes.
Thanks KrOW for library Babel.js for converting ES6 scripts into runnable on pre-ES6 browsers.
3. QUOTE from David:
"In fact, we use the improved syntax for new ECMA features when possible to reduce bugs and future proof our code."
(his comment on Christmas)
Thanks, Gordon. I don't know, maybe I'm over-thinking this and it's only a matter of time and practice. Back to the basics for me. As for David's quote, well... he's not wrong. Everything is evolving in a rapid pace, and developers do need to be able to keep up with the times.
Here is the code comparison
Vasilis Karapas What I could tell you is programmers would like ES6 way to code, if they really understand ES6. Take you time to learn ES6 well, you would like it then.