Ecmascript 6 usage guidelines for Free Code Camp

Having looked up a bit of Javascript documentation as I’m learning it, I’ve come across a lot of useful features that are supported in the newer versions of Javascript (like Ecmascript 6). Unfortunately there still seem to be some browsers in use (like Internet Explorer 11) that don’t support many or most of these features.

My question is: what version of Javascript should I be using when I’m doing Free Code Camp exercises and projects?

Thanks. That’s good to know.

I use Safari, Firefox, and they seem to support ES6.