Multiple calls to state updater from useState in component causes multiple re-renders
You could combine the loading state and data state into one state object and then you could do one setState call and there will only be one render.
Note: Unlike the setState in class components, the setState returned from useState doesn't merge objects with existing state, it replaces the object entirely. If you want to do a merge, you would need to read the previous state and merge it with the new values yourself. Refer to the docs.
I wouldn't worry too much about calling renders excessively until you have determined you have a performance problem. Rendering (in the React context) and committing the virtual DOM updates to the real DOM are different matters. The rendering here is referring to generating virtual DOMs, and not about updating the browser DOM. React may batch the setState calls and update the browser DOM with the final new state.
const {useState, useEffect} = React;function App() { const [userRequest, setUserRequest] = useState({ loading: false, user: null, }); useEffect(() => { // Note that this replaces the entire object and deletes user key! setUserRequest({ loading: true }); fetch('https://randomuser.me/api/') .then(results => results.json()) .then(data => { setUserRequest({ loading: false, user: data.results[0], }); }); }, []); const { loading, user } = userRequest; return ( <div> {loading && 'Loading...'} {user && user.name.first} </div> );}ReactDOM.render(<App />, document.querySelector('#app'));<script src="https://unpkg.com/react@16.7.0-alpha.0/umd/react.development.js"></script><script src="https://unpkg.com/react-dom@16.7.0-alpha.0/umd/react-dom.development.js"></script><div id="app"></div>Alternative - write your own state merger hook
const {useState, useEffect} = React;function useMergeState(initialState) { const [state, setState] = useState(initialState); const setMergedState = newState => setState(prevState => Object.assign({}, prevState, newState) ); return [state, setMergedState];}function App() { const [userRequest, setUserRequest] = useMergeState({ loading: false, user: null, }); useEffect(() => { setUserRequest({ loading: true }); fetch('https://randomuser.me/api/') .then(results => results.json()) .then(data => { setUserRequest({ loading: false, user: data.results[0], }); }); }, []); const { loading, user } = userRequest; return ( <div> {loading && 'Loading...'} {user && user.name.first} </div> );}ReactDOM.render(<App />, document.querySelector('#app'));<script src="https://unpkg.com/react@16.7.0-alpha.0/umd/react.development.js"></script><script src="https://unpkg.com/react-dom@16.7.0-alpha.0/umd/react-dom.development.js"></script><div id="app"></div>
Notice. For those who want to use this answer a lot, I decided to turn it into a library. You can find it here:
Github: https://github.com/thevahidal/react-use-setstate
NPM: https://www.npmjs.com/package/react-use-setstate
This also has another solution using useReducer! first we define our new setState.
const [state, setState] = useReducer( (state, newState) => ({...state, ...newState}), {loading: true, data: null, something: ''})after that we can simply use it like the good old classes this.setState, only without the this!
setState({loading: false, data: test.data.results})As you may noticed in our new setState (just like as what we previously had with this.setState), we don't need to update all the states together! for example I can change one of our states like this (and it doesn't alter other states!):
setState({loading: false})Awesome, Ha?!
So let's put all the pieces together:
import {useReducer} from 'react'const getData = url => { const [state, setState] = useReducer( (state, newState) => ({...state, ...newState}), {loading: true, data: null} ) useEffect(async () => { const test = await api.get('/people') if(test.ok){ setState({loading: false, data: test.data.results}) } }, []) return state}Typescript Support.Thanks to P. Galbraith who replied this solution,Those using typescript can use this:
useReducer<Reducer<MyState, Partial<MyState>>>(...)where MyState is the type of your state object.
e.g. In our case it'll be like this:
interface MyState { loading: boolean; data: any; something: string;}const [state, setState] = useReducer<Reducer<MyState, Partial<MyState>>>( (state, newState) => ({...state, ...newState}), {loading: true, data: null, something: ''})Previous State Support.In comments user2420374 asked for a way to have access to the prevState inside our setState, so here's a way to achieve this goal:
const [state, setState] = useReducer( (state, newState) => { newWithPrevState = isFunction(newState) ? newState(state) : newState return ( {...state, ...newWithPrevState} ) }, initialState)// And then use it like this...setState(prevState => {...})isFunction checks whether the passed argument is a function (which means you're trying to access the prevState) or a plain object. You can find this implementation of isFunction by Alex Grande here.
Batching update in react-hooks https://github.com/facebook/react/issues/14259
React currently will batch state updates if they're triggered from within a React-based event, like a button click or input change. It will not batch updates if they're triggered outside of a React event handler, like an async call.