JAVASCRIPT

prevstate in usestate

const [prevState, setState] = React.useState([]);

setState(prevState => [...prevState, 'somedata'] );

usestate hook with prevstate

const [count, setCount] = useState(0) // count = 0
setCount(prevCount => prevCount + 1) // count = 1

this.setstate prevstate

this.setState(prevState => ({ n: !prevState.n }))