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Docs: Enhance and correct selector memoization example in Essentials Part 6 #4821

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Docs: Enhance and correct selector memoization example in Essentials Part 6 #4821

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8 changes: 7 additions & 1 deletion docs/tutorials/essentials/part-6-performance-normalization.md
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Original file line number Diff line number Diff line change
Expand Up @@ -901,14 +901,20 @@ selectPostsByUser(state1, 'user2')

dispatch(reactionAdded())
const state2 = getState()
// Output selector does not run, because `posts` and `userId` are the same
// Output selector runs, because the `posts` has changed
selectPostsByUser(state2, 'user2')

// Add some more posts
dispatch(addNewPost())
const state3 = getState()
// Output selector runs, because `posts` has changed
selectPostsByUser(state3, 'user2')

// Fetch notifications
dispatch(fetchNotifications())
const state4 = getState()
// Output selector does not run, because `posts` and `userId` are the same
selectPostsByUser(state4, 'user2')
```
Now that we've memoized `selectPostsByUser`, we can try repeating the React profiler with `<UserPage>` open while fetching notifications. This time we should see that `<UserPage>` doesn't re-render:
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