React · Middle · Question 73 of 75

Why shouldn't you read or write `ref.current` during render?

✓Correct answer: It makes rendering impure and unpredictable; refs are meant for event handlers and effects
2It throws an error in production
3Refs are null until the app is unmounted

Explanation

The exception is lazy initialization: if (ref.current === null) ref.current = new Thing(). Otherwise React can't know about the change.

Further reading

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