[IgorPartola]

So think of it this way: you want to avoid calling malloc() to increase performance. JavaScript does not have the semantics to avoid this. You also want to avoid looping. JavaScript does not have the semantics to avoid it.

If you haven’t had experience with actual performant code JS can seem fast. But it’s is a Huffy bike compared to a Kawasaki H2. Sure it is better than a kid’s trike but it is not a performance system by any stretch of the imagination. You use JS for convenience, not performance.

[gbuk2013]

IIRC V8 actually does some tricks under the hood to avoid malocs which is why Node.js can be be unexpectedly fast (I saw some benchmarks where it was only 4x of equivalent C code) - for example it recycles objects of the same shape (which is why it is beneficial not to modify object structure in hot code paths).

[yencabulator]

JITs are a great magic trick but it's nowhere near guaranteed you'll get good steady performance out of one, especially when the workload is wide not narrow.

https://arxiv.org/abs/1602.00602v1

[hinkley]

Hidden classes is a whoooole thing. I’ve switched several projects to Maps for lookup tables so as not to poke that bear. Storage is the unhappy path for this.

[winrid]

(to be fair the memory manager reuses memory, so it's not calling out to malloc all the time, but yes a manually-managed impl. will be much more efficient)

[IgorPartola]

Whichever way you manage memory, it is overhead. But the main problem is the language does not have zero copy semantics so lots of things trigger a memcpy(). But if you also need to call malloc() or even worse if you have to make syscalls you are hosed. Syscalls aren’t just functions, they require a whole lot of orchestration to make happen.

JavaScript engines also are also JITted which is better than a straight interpreter but except microbenchmarks worse than compiled code.

I use it for nearly all my projects. It is fine for most UI stuff and is OK for some server stuff (though Python is superior in every way). But would never want to replace something like nginx with a JavaScript based web server.

[winrid]

V8 does a lot of things to prevent copies. If you create two strings and concat them and assigned to a third var, no copy happens (c = a+b, c is a rope). Objects are by reference... Strings are interned.. the main gotcha with copies is when you need to convert from internal representation (utf16) to utf8 for outputs, it will copy then.