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implementation with useContextSelector (Experimental) ⚠️ #1350

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commented Jul 8, 2019

This PR implements the connect api for and hooks apis using a proposed RFC: Context Selectors

This is not an official React API


The point of this PR is to illustrate how libraries can shrink and become less complicated with this proposed API change. Please note not all tests pass because not all tests are relevant. It's possible there are edge case bugs too, this PR is for exploration and illustration, not for merging.


  • This implementation is almost as fast as v7, significantly faster than v6. It should be eminently usable
  • It supports concurrent mode correctly
  • It does not suffer zombie child problems, including with hooks use
  • It is significantly smaller
  • It is significantly simpler

How to use

get a working copy of react with useContextSelector

  1. clone gnoff/react#3 and checkout branch
  2. run yarn build (will take a while)
  3. run cd build/node_modules/react && npm link
  4. run cd ../react-dom && npm link

checkout this react-redux branch

  1. checkout gnoff-context-selectors
  2. run npm link react react-dom
  3. run tests to confirm things worked npx jest (some tests fail but you should get most passing)

Quick Access

You can see a built version of both the react and react-redux lib here:

gzip sizes

master: around 5.69kb
this PR: around 4.39kb

these sizes should be smaller in real bundles if dependency deduping is working correctly. this means that relative decrease in size should be magnified


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commented Jul 8, 2019

@markerikson here it is, properly described :)


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commented Jul 8, 2019

Deploy preview for react-redux-docs ready!

Built with commit bfaef05


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commented Jul 8, 2019

Thanks, I'll try to look at it later.

The immediate observation I'd make is that from a project management standpoint, this would effectively require another major, because:

  • We'd have to require React 16.whatevernnewnewcontext as a minimum peer dep
  • As we found out with v6, while it's not part of our public API, folks do currently rely on the "tearing" behavior where dispatched actions during mount are immediately visible in mounting child components. Reading a consistent state value from context actually breaks that expectation (especially important for SSR and dynamic reducer loading - see #1107 and #1150 ). Not saying it's a blocker, but if we do go for context-based state updates, we would need to consider that issue.
@brunolemos brunolemos referenced this pull request Jul 8, 2019

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commented Jul 8, 2019

Thanks Mark,

Definitely would require a new major, no question there.

as for tearing, that's an interesting problem. Unfortunately I don't think there is a way for concurrent react support to exist and still have tearing support. On the flip side maybe when concurrent react is mature there will be a way to lean into it. Imagine yielding the render once a dispatch occurred so you could restart it with the updated state value. It would still be possible to get yourself into trouble but that true today too :)

The SSR bit is interesting, are you saying that because you need to synchronously render everything, mounted based dispatches need to be visible to children b/c there is no opportunity to wait for a second render to resolve things?

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