In general is it better to use one or many useEffect hooks in a single component? [closed]

Question

I have some side effects to apply in my react component and want to know how to organize them:

• as a single useEffect
• or several useEffects

Which is better in terms of performance and architecture?

Answer 1

The pattern that you need to follow depends on your use case.

First: You might have a situation where you need to add event listener during the initial mount and clean them up at unmount and another case where a particular listener needs to be cleaned up and re-added on a prop change.

In such a case, using two different useEffect is better to keep the relevant logic together as well as having performance benefits

useEffect(() => {
   // adding event listeners on mount here
   return () => {
       // cleaning up the listeners here
   }
}, []);

useEffect(() => {
   // adding listeners everytime props.x changes
   return () => {
       // removing the listener when props.x changes
   }
}, [props.x])

Second: You need to trigger an API call or some other side-effect when any of the state or props change from a defined set. In such a case a single useEffect with the relevant dependencies to monitor would be better

useEffect(() => {
    // side effect here on change of any of props.x or stateY
}, [props.x, stateY])

Third: You need separate side-effect for different sets of changes. In such a case, separate out relevant side-effects into different useEffects

useEffect(() => {
   // some side-effect on change of props.x
}, [props.x])

useEffect(() => {
   // another side-effect on change of stateX or stateY 
}, [stateX, stateY])