why use prevstate react code example

Example 1: react prevstate

handleClick() {
  this.setState(prevState => ({
    isToggleOn: !prevState.isToggleOn
  }));
}

Example 2: prevstate in usestate

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

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

Example 3: this.setstate prevstate

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