How to use componentWillMount() in React Hooks?

Understanding useEffect and class component lifecycle parallels

The journey to mastering functional components starts by unraveling how useEffect relates to the classic lifecycle methods you're used to in class components.

Lifecycle hooks with useEffect

useEffect is Hercules in disguise—it does three jobs in one. With an empty array ([ ]), it operates like componentDidMount, raring to go after the first render. With no second argument, it's on its toes, pulling a componentDidUpdate after every render. If you pass it specific dependencies, it does a componentDidUpdate impersonation and just runs when those dependencies change.

Cleanup and unmounting behavior

For tidying up after itself, like a well-trained pet, useEffect allows for a cleanup function. Now, who's a good boy?

useEffect(() => {
  // Who left the chat? Add an event listener or other side effect here
  
  return () => {
    // Operation cleanup, everyone out of the pool! Clean up event listeners or other subscriptions here
  };
}, []); // Once more, with feeling! It still runs only once


First-render-only patterns

For situations where only the componentWillMount vibe will do, use a useRef and toggle whether effects run just on the first render, or if they need to run on updates too. This investment pays off, promise! Investing in the first render instead of the mount gives a whole new meaning to early retirement.

const mountedRef = useRef(false);

useEffect(() => {
  if (!mountedRef.current) {
    mountedRef.current = true;
    // Do the "componentWillMount" victory dance here
  }
}, []);


Performance optimizations

It's not all fun and games. For preventing additional re-renders in the spirit of shouldComponentUpdate, be sure to useCallback for creating memoized callback functions and useMemo for memoizing values when the dependencies change.

When not to mimic componentWillMount

Yes, useEffect is amazing, but it's not a cure-all. There are distinct situations where different solutions are the better choice.

Data fetching and side effects

Fetch data and initiate side effects with useEffect after the component mounts. This is to ensure the hooks get set up just as you like them and without errors.

Managing complex state and logic

Break down complex state and logic interactions into smaller, easy-to-suck-on candy units. This makes code more legible and maintainable, keeping the headaches at bay. You can thank me later.

Infinite loop prevention

Don't forget to specify dependencies in the second argument of useEffect to prevent infinite loops of re-renders and state updates.

Caveats and considerations

React isn't only about mounting and rendering; it's essential to consider how misuse of useEffect can introduce bugs. It's fine to use older patterns, but make sure they're the right fit for your need before including them.

References

1. Using the Effect Hook – React — To understand effects better than my mom understands me,
2. Hooks API Reference – React — Know your hooks like the back of your hand,
3. Introducing Hooks – React — No better place to get started on hooks,
4. Making Sense of React Hooks — What's behind door number three? A comprehensive explanation of hooks by Dan Abramov,
5. How to fetch data with React Hooks — Catching on how to fetch data like a pro,
6. useEffect vs useLayoutEffect — The age-long battle between useEffect and useLayoutEffect for the pre-render logic supremacy,
7. Using promises - JavaScript | MDN — How to dance with promises in JavaScript without stepping on any toes,