State Management · Senior · Question 67 of 75

When does `useSelector(selector, shallowEqual)` help?

const { name, email } = useSelector((s) => ({ name: s.user.name, email: s.user.email }), shallowEqual);

✓Correct answer: When the selector returns a new object/array each time but its fields are often equal
2Always - it should be used for every selector
3When the selector returns a primitive

Explanation

Without it, the new object fails === and re-renders on every action. Alternatives: select primitives separately or use a memoized selector.

Further reading

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