06.useReducer源码实现

hooks.js

export function useReducer(reducer, initialValue) {
  states[hookIndex] = states[hookIndex] || initialValue;
  const currentIndex = hookIndex;
  function dispatch(action) {
    states[currentIndex] = reducer(states[currentIndex], action);;
    emitUpdateForHooks();
  }
  return [states[hookIndex++], dispatch];
}