Think of your useEffect as a mix of componentDidMount, componentDidUpdate, and componentWillUnmount, as stated in the React documentation. To behave like componentDidMount, you would need to set your useEffect like this: useEffect(() => console.log(‘mounted’), []); The first argument is a callback that will be fired based on the second argument, which is an array of … Read more
You need to clear your interval, useEffect(() => { const intervalId = setInterval(() => { //assign interval to a variable to clear it. setState(state => ({ data: state.data, error: false, loading: true })) fetch(url) .then(data => data.json()) .then(obj => Object.keys(obj).map(key => { let newData = obj[key] newData.key = key return newData }) ) .then(newData => … Read more
Ok I will try to clear your confusion. If you have some components like this <A> <B /> </A> Then on the first load (Reload) log will be Child B useEffect Parent A useEffect Then lets say you navigate to some route and then go to Child component log will be Child B useEffect Parent … Read more
June 2022 update (still accurate at end of 2023): React 18 has removed this warning message, and the workarounds to get rid of it may no longer be necessary. Part of the reason they removed it is that it has always been a bit misleading. It says you have a memory leak, but often times … Read more
Everything I can find on this seems to link back to this github issue circa 2016. I’ll quote verbatim from there since it doesn’t appear to have been covered on Stack Overflow before and it explains things pretty thoroughly: .then(() => { this.setState({ loaded: true }) }) .catch(()=> { console.log(‘Swallowed!’) }); Your catch() handler is … Read more
I can’t answer the “should you” part of whether to use refs for this instead other than if you do, you don’t need those id values unless you use them for something else. But here’s how you would: Use useRef(null) to create the ref. const activeSlideRef = useRef(null); Put it on the Slide that’s currently … Read more
Your useEffect is executed only once per render cycle, but you have several state updates in your useEffect which cause a re-render. Hence you get a lot of alerts. See a demo of your code and see the console.logs as well as comments Also note that useEffect will when you provide empty array dependency, your … Read more
You’re returning the result of calling getResponse() from the useEffect function. If you return anything from useEffect, it has to be a function. Changing your code to this should fix it because you’re no longer returning anything from the useEffect function. useEffect(() => { getResponse(); }); The useEffect Cleanup Function If you return anything from … Read more
About useEffect hook: By using this Hook, you tell React that your component needs to do something after render. React will remember the function you passed (we’ll refer to it as our “effect”), and call it later after performing the DOM updates. more This means that function inside useEffect will be called after rendering of … Read more