This happens because useEffect is triggered after every render, which is the invocation of the Counter() function in this case of functional components. When you do a setX call returned from useState in a useEffect, React will render that component again, and useEffect will run again. This causes an infinite loop: Counter() → useEffect() → … Read more
React performs the cleanup when the component unmounts. I’m not sure where you read this but this statement is incorrect. React performs the cleanup when the dependencies to that hook changes and the effect hook needs to run again with new values. This behaviour is intentional to maintain the reactivity of the view to changing … Read more
You can put the handleKeyUp function inside of the function given to useEffect (which is the recommended way of doing it according to the official documentation) and only add the listener and return a cleanup function when collapsed is false. useEffect(() => { if (collapsed) { return; } function handleKeyUp(event) { switch (event.key) { case … Read more
clearly going to be reassigned to a different primitive value Not really. When the component is rerendered, the function is executed again, creating a new scope, creating a new count variable, which has nothing to do with the previous variable. Example: let _state; let _initialized = false; function useState(initialValue) { if (!_initialized) { _state = … Read more
For objects you can use the spread operator to use prevState within your setState call. const [object, setObject] = useState({ firstKey: ”, secondKey: ”, }); setObject((prevState) => ({ …prevState, secondKey: ‘value’, })); // object = { // firstKey: ”, // secondKey: ‘value’, // } The snippet below show an example of using prevState for setting … Read more
Redux is a library that encourages data flow in a specific manner. react-redux on the other hand implements the React friendly approach and provides a lot middlewares and wrappers so that the library consumers do not have to set up the entire process on their own. While useReducer is a part of how Redux works, … Read more
React hook makes use of hidden state of a component, it’s stored inside a fiber, a fiber is an entity that corresponds to component instance (in a broader sense, because functional components don’t create instances as class components). It’s React renderer that gives a hook the access to respective context, state, etc. and incidentally, it’s … Read more
export default () => { const [isSending, setIsSending] = useState(false) const sendRequest = useCallback(async () => { // don’t send again while we are sending if (isSending) return // update state setIsSending(true) // send the actual request await API.sendRequest() // once the request is sent, update state again setIsSending(false) }, [isSending]) // update the callback … Read more
In a comment above Gabriele Petrioli links to the React.memo documentation that explains how to implement shouldComponentUpdate. I was googling combinations of shouldComponentUpdate + useEffect + “react hooks”, and this came up as the result. So after solving my problem with the linked documentation I thought I would bring the information here as well. This … Read more
Load the hook as a module. Then mock the module: jest.mock(‘module_name’, () => ({ useClientRect: () => [300, 200, jest.fn()] })); mock should be called on top of the file outside test fn. Therefore we are going to have only one array as the mocked value. If you want to mock the hook with different … Read more