React · Middle · Question 40 of 75

Why does this selector cause a re-render on any action in the store?

const done = useSelector(state =>
  state.todos.filter(t => t.done)
);

✓Correct answer: filter returns a new array every time
2useSelector always re-renders on any action
3filter is too slow to call inside a selector

Explanation

useSelector runs after every dispatch and compares the result by reference. A new array never equals the previous one. The fix is a memoized createSelector selector, which returns the same array as long as state.todos hasn't changed.

Why does this selector cause a re-render on any action in the store?

Explanation

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