[@types/react] React.creatContext should receive a optional value

[wszgxa]

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DOC: https://reactjs.org/docs/context.html#reactcreatecontext

The defaultValue argument is only used when a component does not have a matching Provider above it in the tree.

And there is an article with this issue, use a tricky way to avoid this problem.

[typescript-bot]

@wszgxa Thank you for submitting this PR!

🔔 @johnnyreilly @bbenezech @pzavolinsky @digiguru @ericanderson @tkrotoff @DovydasNavickas @onigoetz @theruther4d @guilhermehubner @ferdaber @jrakotoharisoa @pascaloliv @Hotell @franklixuefei @Jessidhia @pshrmn @saranshkataria @lukyth @eps1lon - please review this PR in the next few days. Be sure to explicitly select Approve or Request Changes in the GitHub UI so I know what's going on.

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[typescript-bot]

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[eps1lon]

Isn't the problem with this that I can create a context with const Context = createContext<SomeValue>() and then useContext(Context) would return SomeValue instead of SomeValue | undefined? That doesn't sound desirable. I'd rather have opt-out of strict types instead of opt-in to strict types.

[ferdaber]

@eps1lon 's reasoning is correct. We chose to explicitly not include defaultValue as optional even when considering the docs. The React team also does not consider defaultValue to be itself optional. Let me see if I can pull up the old PR...

[ferdaber]

#24509 (comment)