That's ES6 JavaScript (running on Node 0.11.15). We've already migrated most of our production code to this and we're loving it!

If you like that kind of control flow, check out the library we wrote to do it: https://github.com/storehouse/engen

Why not use let instead of var?

Only habit. We're so used to var. But yea, need to transition to let for most things.

I think migrating to const makes more sense. In practice only a few things require to be mutated.

Didn't realize const was in. Will definitely be using it.

I believe that's Javascript (ES6).