diode VS luajit

I've started with scalajs-react. Overall the experience was good (perhaps the overloaded API is my biggest concern, but we can live with that). Then I stumbled upon a problem where I need to propagate a state change from two leaf components and found out I need something like this Redux thing. I trtied built-in StateSnapshot, but couldn't make it working. Then I googled for Scala-land alternatives and it seems like there are few semi-abandoned Redux facades and Diode. Diode looks like what I need, but:

c) Diode is my favourite "wiring" library. It is similar to Redux and allows you to handle asynchronous behaviour in your frontend. It has a learning curve but it's not too bad and makes everything so much easier.

Japgolly has put a ton of time and care into https://github.com/japgolly/scalajs-react which is a complete React binding in scalajs. This paired with something like Diode (https://github.com/suzaku-io/diode) and you get a full frontend solution in scalajs.

> No offence, but have you written any compilers or interpreters?

I have, but nothing sophisticated.

> The points that you discuss [...] may be performance concerns for application developers [...] but they have very little to do with the optimisations you can make as a compiler/interpreter writer. [...] The only one that's somewhat relevant is 'global scope by default'

I didn't mean to imply that these where the three common traits that make both Javascript and Lua particularly hard to optimize, I just picked them as examples for how Javascript and Lua are closer to each other than most other dynamic languages.

But let's dig in a bit on your claim that things like all numbers being doubles or having a array cum map cum record type has very little to do with the optimizations you can make as a compiler/interpreter writer, because it sure seems to me that LuaJIT and V8 do a bunch of optimizations around these things. Both have dual number representations under the hood and will try to avoid representing numbers that remain in the domain of 32 bit integers as double values internally when that gives performance gains. The logic for figuring out if that's the case doesn't seem to be super-straightforward or target architecture independent from looking at the comments in <https://github.com/LuaDist/luajit/blob/master/src/lj_opt_nar...>.

LuaJIT furthermore uses NaN tagging (as do some JS engines, although not V8), which looks less attractive to me as a representation strategy if your numbers are not all/mostly notional doubles (as is indeed the case in newer version of Lua where 64bit integers are the dominant number type)

Also, as far as the super-flexible lua tables are concerned, I'm pretty sure LuaJIT goes through some amount of trouble to specialize various common use cases of tables, e.g. as arrays without holes, and surprise, so does V8 (https://v8.dev/blog/fast-properties#elements-or-array-indexe...). I don't think you'd find something equivalent in a high performance scheme implementation.

> but this doesn't touch the surface of the issues that make JS hard to optimise, such as the fact that your, say, memoisation of an object property or method may be broken by an `eval` call of an arbitrary runtime value somewhere else in the code (which, due to asynchronicity, could take place at more or less any time from the point of view of your given 'peephole').

Eval belongs to a core set of features that basically all popular dynamic languages share that presents headaches for high performance implementations. How is Javascript's eval particularly problematic in this regard, and specifically much more so than Lua's loadstring/load?

More generally what do you think makes (pre-ES6) javascript significantly harder to optimize than lua 5.0?