If your React app uses AJAX to fetch initial data from an API, which lifecycle method is best to use?

If your React app uses AJAX to fetch initial data from an API, which lifecycle method is best to use?

• A. ComponentDidMount
• B. ComponentWillMount
• C. Render
• D. ComponentWillUpdate

Answer: (A)

Fetching data after the component has been mounted is the correct approach because AJAX is a side effect you want to run only once the component exists in the DOM. The lifecycle method that runs right after mounting is designed for this kind of operation. It gives you a safe moment to start asynchronous requests and then update the component’s state with the received data, which triggers a re-render to show the fetched information. Doing the fetch earlier, before the component is mounted, can lead to inconsistencies and is discouraged in modern React because render should remain pure and side-effect free. Fetching during the render itself is also a bad idea since rendering should only describe what UI should look like, not perform network requests. The update lifecycle is intended for responding to changes after the initial render, not for the initial data fetch. If you’re using functional components instead of class components, you’d achieve the same effect with a useEffect hook that runs once on mount.

Fetching data after the component has been mounted is the correct approach because AJAX is a side effect you want to run only once the component exists in the DOM. The lifecycle method that runs right after mounting is designed for this kind of operation. It gives you a safe moment to start asynchronous requests and then update the component’s state with the received data, which triggers a re-render to show the fetched information.

Doing the fetch earlier, before the component is mounted, can lead to inconsistencies and is discouraged in modern React because render should remain pure and side-effect free. Fetching during the render itself is also a bad idea since rendering should only describe what UI should look like, not perform network requests. The update lifecycle is intended for responding to changes after the initial render, not for the initial data fetch.

If you’re using functional components instead of class components, you’d achieve the same effect with a useEffect hook that runs once on mount.