There is one hook used most commonly with the React function component. The hook is called the useEffect hook. This hook is used to tell React that your component needs to do something after rendering.

There is one mistake commonly made when using useEffect. It won’t look much at the beginning but the issues it creates are very difficult to debug.

The mystery of `useEffect` dependencies

The useEffect hook accepts a list of dependencies. It tells React that whenever any of the dependencies changes, execute the callback function passed.

This is where the mistake is made. React provides a hook called useRef hook. The useRef hook is used when you want to keep track of a value. The special thing about this hook is that it doesn’t trigger a re-render when the value is updated.

With useRef hook the React guarantees that the object returned will be stored and associated with the current instance of the component as long as that component exists.

It is not a good practice to use useRef the value inside the list of dependencies passed to useEffect. Since the useRef object instance never changes as long as the component exists, using that in the list of dependencies will not execute the useEffect callback.

Also using the ref.current in the list of dependencies is not a good idea because it will lead to surprising behaviour that's difficult to debug.

A close look at bug created with `useEffect`

Below app uses ref.current inside the list of dependencies. Check out the surprising behaviour that leads to a bug. The code looks straightforward at the top, but under the hook, it’s creating a bug just because or ref.current in the list of dependencies. The useEffect hook is not executing and updating the state when used ref.current as a dependency.

https://codesandbox.io/s/useeffect-depends-on-useref-forked-q045p2

A simple method to avoid this bug easily

Use this thumb rule and you won’t encounter this bug in the future: Never use those things in your useEffect dependency array that won't trigger a re-render when updated. Dependencies should only include values that participate in top-down React data flow. Such as props, state, and what you calculate from them.

Do you make this mistake with useEffect in React?

There is one hook used most commonly with the React function component. The hook is called

What will you write today?