OK, some stuff is nice (async), but seems like the standard keeps adding syntactic sugar while not addressing more pressing daily challenges, i.e. deep cloning (Object.assign does not go deep).
Very few languages that I know have deep cloning outside of some sort of serialization hack anyway (C#'s deep cloning is a reuse of/leftover from binary marshalling), so this is roughly par for the course, so far as I'm aware.
Relatively short, but IMO not relatively performant. All the JSON encoding/decoding takes its toll.
Obviously YMMV, and your performance needs likely differ from my own.
(Personally, at this point I try to use immutability [with ImmutableJS or friends] over deep cloning, but sometimes a deep clone is still handy.)