Document useContext bailout strategy (#1848)

gaearon · web-flow · commit b1bc193dbad4 · 2019-03-19T22:09:21.000Z
diff --git a/content/docs/hooks-reference.md b/content/docs/hooks-reference.md
@@ -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>`.

Original file line number	Diff line number	Diff line change
@@ -188,6 +188,8 @@ Don't forget that the argument to `useContext` must be the *context object itsel
`188`	`188`	* Incorrect: `useContext(MyContext.Consumer)`
`189`	`189`	* Incorrect: `useContext(MyContext.Provider)`
`190`	`190`
	`191`	+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).
	`192`	`+`
`191`	`193`	`>Tip`
`192`	`194`	`>`
`193`	`195`	>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>`.