6to5 has been mostly pain-free for me. Getting it to play nicely with my code coverage tool was a bit tricky, but aside from that it wasn't bad at all. Bear i

6to5 has been mostly pain-free for me. Getting it to play nicely with my code coverage tool was a bit tricky, but aside from that it wasn't bad at all. Bear in mind that ES6 is fully backwards-compatible with ES5, so you can set up a transpiler without having to actually rewrite your whole codebase right off the bat. It's pretty easy to upgrade gradually if you need or want to.