from Hacker News

Array Concat vs. Spread

by laex on 7/29/20, 6:28 AM with 1 comments

• by Asraelite on 7/29/20, 4:31 PM

  I've always found it somewhat confusing how common operations like this with identical behavior but differing syntax can have such drastic differences in speed. Another example would be `for (let i in array) { array[i]...` versus `array.forEach(...`.

  For highly optimized engines like V8 and SpiderMonkey, it seems like recognizing these cases and automatically substituting in the faster behavior would be pretty low hanging fruit that could have a significant impact on existing scripts' performance.

  Maybe there's some underlying reason to do with how these engines work internally that prevents such optimizations from easily being performed though.