Haha, I think that was a one time fluke! :D

I'm aiming for something like 75-85% this year; basically get iterators properly done (they're in the engine but not very complete yet), implement ECMAScript modules, and then mostly focus on correctness, builtins, and performance improvements after that. 99% would perhaps be possible by the end of next year, barring unforeseeable surprises.

have you considered using js polyfills to help you get closer to 100% coverage and then replacing with native implementations prioritized by performance impact?

Not really, no. Its an interesting proposition, but for the most part I believe I'll be sticking it out the "hard way". The ECMAScript spec is fairly easy to read as well, after all. (Nevermind that I spent the single free hour I had today cursing at my incapability of understanding what is going wrong with my iterator code and what it even should do vis-à-vis the spec :D )