React: Known pain-points around signal initialization

Learning
1

Hello, I’m running into an issue in React where I do (essentially):

React.S.(value (map f some_signal))

And this blows up because the signal returned by map is not initialized.

In reality, I’m doing ReactiveData.from_signal here, which uses React.S.value.

I saw in the Note repo, in talking about the Pro’s of Note:

  • Provides (hopefully) a better combinator set. Especially with respect to the pain point of signal initialization in React: in Note, due the pull based strategy, {E,S}.value is safe and sound to use.

What is going on here? Is there a way around it in React?

2

I found Your production web stack in 2020 - #10 by smondet which references the .value traps.

In my case I tried changing it to ReactiveData.from_signal (React.S.fmap f [] some_signal) which at least avoid the exception, but the list doesn’t seem to change with my signal getting updated (at least in my test case).

3

value is unsafe in React the proper way of getting a signal value is to bind.

4

Thank you.

Is there a safe way to combine ReactiveData.Rlist.from_signal? Or is that function inherently unsafe and should be avoided?

5

I don’t know I’m not the author of ReactiveData.

6

Whoops, sorry, I made an assumption.

What I’ve done, which seems to work is something like:

let (signal, set) = create default_value in
let workaround = map (fun v -> set v) signal in
from_signal @@ map (fun v -> stuff I want to do) signal

Not ideal but the create in the version of React I’m using seems to guarantee there is a value there so it unblocks me until I find a more elegant solution.

Thank you for the quick response, @dbuenzli