Afaik much JS these days is optimised, see things like V8's turbofan https://v8.dev/blog/turbofan-jit https://v8.dev/blog/turbofan-jit However there is definit

Afaik much JS these days is optimised, see things like V8's turbofan https://v8.dev/blog/turbofan-jit https://v8.dev/blog/turbofan-jit However there is definitely still less intrinsic optimisation from a dev perspective I think - people will iterate over the same array multiple times in different places rather than do it once. I guess our industry has decided moving faster is better than running faster for a lot of stuff.