I've used these things. IME, nowadays it's not worth the bundle size to bring in these libraries. map/filter seems quite optimized, {...obj} is fast since its only shallow. Yes it does come down to practices vs better libraries, but in practice, it's fine IME

One thing to note, i was very excited that we have a bunch of lazy methods on Iterator protocol, but they are slow as shit as of earlier this year.

I wrote a parser a year ago with extreme use of .map (every step of processing was cloning the tokens), and i thought, let's migrate it to lazy iterator - it got ~10x slower :(. The compile time was fine for my use cases, so i didn't give immutable-js a try, but it was a surprise

I did some benchmarks on map+filter vs mutable for of + push, and on firefox up to 200-300 elements map+filter is actually faster (unforunately not on chrome).

Of course, its not the best, but my experience is that modern js engines are fast enough for most use cases to not have to bring in any libraries anymore