That explains why Electron apps and Web pages are slow but the post you're replying to is about games...

Ok fair enough, but the mindset is spreading: json (javascript) parsing is what caused GTA Online loading times to balloon and I dread playing Call of Duty online as it wants to download and install dozens of GBs every time I launch it.

It wasn’t json parsing per se, but a buggy roll-your-own implementation that used a function (sscanf iirc) with a surprising nontrivial complexity on a long string. Fun part is, if they just outsourced that load to javascript and its JSON.parse, they’d never encounter that exponential slowdown. Javascript is a nice target to blame, but it isn’t the problem. CPUs got hundreds of times faster, javascript only divides it by N, which stays low and constant (at least) through decades. Do you really believe that if browsers only supported MSVC++-based DLLs without scripting, sites would run faster? That would be naive.

You may be thinking of GTA Online, but the point is still valid.

Games do use JS, some UIs actually render using a webview (Unity etc is capable of this)

I didn't see anyone complaining about games in the parent comments.

Afaik much JS these days is optimised, see things like V8's turbofan 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.