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Document useContext bailout strategy (#1848)

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Dan Abramov
2019-03-19 22:09:21 +00:00
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content/docs/hooks-reference.md
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@@ -188,6 +188,8 @@ Don't forget that the argument to `useContext` must be the *context object itsel
* **Incorrect:** `useContext(MyContext.Consumer)`
* **Incorrect:** `useContext(MyContext.Provider)`
A component calling `useContext` will always re-render when the context value changes. If re-rendering the component is expensive, you can [optimize it by using memoization](https://github.com/facebook/react/issues/15156#issuecomment-474590693).
>Tip
>
>If you're familiar with the context API before Hooks, `useContext(MyContext)` is equivalent to `static contextType = MyContext` in a class, or to `<MyContext.Consumer>`.