React hooks: accessing up-to-date state from within a callback

Question

EDIT (22 June 2020): as this question has some renewed interest, I realise there may be a few points of confusion. So I would like to highlight: the example in the question

Answer 1

You can access the latest state in setState callback. But the intention is not clear, we never want to setState in this case, it may confuse other people when they read your code. So you may want to wrap it in another hook that can express what you want better

function useExtendedState(initialState: T) {
  const [state, setState] = React.useState(initialState);
  const getLatestState = () => {
    return new Promise((resolve, reject) => {
      setState((s) => {
        resolve(s);
        return s;
      });
    });
  };

  return [state, setState, getLatestState] as const;
}

Usage

const [counter, setCounter, getCounter] = useExtendedState(0);

...

getCounter().then((counter) => /* ... */)

// you can also use await in async callback
const counter = await getCounter();

Live Demo