AI solution for React Quiz on BFE.dev
21. useEffect() II

The code outputs the following by console.log:

true
false

This is because useIsMounted hook returns the value of isMounted.current, which is initially set to false. After rendering the Child component, the useEffect hook runs and sets the value of isMounted.current to true. The first console.log statement in the useEffect hook logs the initial value of isMounted.current, which is true. Then, a promise is resolved, and the second console.log statement logs the new value of isMounted.current, which is false. This is because the unmount function passed from the parent component was called, unregistering the component from the DOM and causing useIsMounted to return false.