ES8, actually! My latest project is adding a --install flag for eshost-cli to install javascript hosts from public file shares so you can use the tool without manually downloading or compiling your own from source. I struggled with putting the logic into promises, but because it's really branchy and includes loops, it was very hard to reason about. Using async functions instead made it almost trivial! I love that feature (and not just because I championed it ;)). Yeah, now I have a node 8 dependency, but I could fix that with a transpiler if I cared enough.