spike: some experiments on use(obserable) - very rough

[coolsoftwaretyler]

Extremely rough, actual implementation code that isn't even close to working.

Run test:

yarn install
yarn test packages/react-reconciler/src/__tests__/ReactUseObservable-test.js

[coolsoftwaretyler]

For more context, see https://coolsoftware.dev/blog/a-path-towards-observable-values-in-react/

[coolsoftwaretyler]

The diff looks bigger than it is because my editor formatted it, but you'll wanna look for the use<T function, or readObservable for new code

[coolsoftwaretyler]

This is the beginning of the relevant changes

[coolsoftwaretyler]

In 7c40b75, I just started logging the name value in Sync, and the output when you run the test contains:

Running tests for default (experimental)...
  console.log
    name First

      at Sync (packages/react-reconciler/src/__tests__/ReactUseObservable-test.js:97:15)

  console.log
    name Second

      at Sync (packages/react-reconciler/src/__tests__/ReactUseObservable-test.js:97:15)

I also changed the names to First and Second for more clarity.

So it seems like the observability is working, but I'm making a silly mistake in the test here.

[coolsoftwaretyler]

Hey @rcharmeyer - can you say more about what you mean here?

[rcharmeyer]

Hey @rcharmeyer - can you say more about what you mean here?

Nevermind, I was just hallucinating a use case that doesn't exist.

[coolsoftwaretyler]

Hey @rcharmeyer - can you say more about what you mean here?

Nevermind, I was just hallucinating a use case that doesn't exist.

Haha I 100% understand. The last few days have been full of that for me. Thanks for taking a look anyway! If you know more about React internals than me, I'd appreciate any insights you have.

[coolsoftwaretyler]

Heyo, I think I got it.

Since this hacky code doesn't know anything about memoizedProps and React doesn't know about it, the reconciler was bailing out early. That's why the console logs ran (ahead of the actual reconciliation step), but the output wouldn't update in test rendered output or when I was demoing in a real browser.

So now the callback calls fiber.memoizedProps = null which strikes me as 100% not the way this should be handled.

But, it makes this demo minimally functional. Run yarn test packages/react-reconciler/src/__tests__/ReactUseObservable-test.js and see that updating the observed value gets it to update the rendered output.

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