What is the purpose of the cleanup function returned from useEffect?

What is the purpose of the cleanup function returned from useEffect?

• A. It runs before the next effect runs or on unmount to clean up resources.
• B. It re-runs the effect multiple times.
• C. It updates the state after the effect finishes.
• D. It redefines the dependencies array.

Answer: (A)

The cleanup function returned by useEffect is for tearing down what the effect did. It runs right before React applies the effect again (when dependencies change) and also when the component unmounts. This lets you release resources the effect set up—like unsubscribing from a data source, clearing a timer, or removing an event listener—so you don’t leak memory or keep outdated work around. It isn’t used to re-run the effect, update state after the effect finishes, or redefine the dependencies array. Those aspects are controlled by the effect’s execution and its dependencies, while the cleanup function’s job is simply to clean up what was created.

The cleanup function returned by useEffect is for tearing down what the effect did. It runs right before React applies the effect again (when dependencies change) and also when the component unmounts. This lets you release resources the effect set up—like unsubscribing from a data source, clearing a timer, or removing an event listener—so you don’t leak memory or keep outdated work around.

It isn’t used to re-run the effect, update state after the effect finishes, or redefine the dependencies array. Those aspects are controlled by the effect’s execution and its dependencies, while the cleanup function’s job is simply to clean up what was created.