React setState + Where does 'prevState' come from?

Question

I just started learning React and JavaScript.
While going through the tutorial, I got to this example code of a component, which creates a toggle button.
This is part of

Answer 1

Im use this. (Example)

const [modal, setModal] = useState(false);
const [dataAction, setDataAction] = useState({name: '', description: ''});

const _handleChangeName = (data) => {
    if(data.name)
        setDataAction( prevState  => ({ ...prevState,   name : data.name }));
    if(data.description)
        setDataAction( prevState  => ({ ...prevState,   description : data.description }));
  };