useReducer

useState 的替代方案。 接受类型为 (state, action) => newState 的 reducer，并返回与 dispatch 方法配对的当前状态。 （如果你熟悉 Redux，你已经知道它是如何工作的。）
下面例子 useState 部分的计数器示例，重写为使用 reducer：

import { useReducer } from 'rax';

const initialState = {count: 0};

function reducer(state, action) {
  switch (action.type) {
	case 'reset':
	  return initialState;
	case 'increment':
	  return {count: state.count + 1};
	case 'decrement':
	  return {count: state.count - 1};
	default:
	  // A reducer must always return a valid state.
	  // Alternatively you can throw an error if an invalid action is dispatched.
	  return state;
  }
}

function Counter({initialCount}) {
  const [state, dispatch] = useReducer(reducer, {count: initialCount});
  return (
	<>
	  Count: {state.count}
	  <button onClick={() => dispatch({type: 'reset'})}>
		Reset
	  </button>
	  <button onClick={() => dispatch({type: 'increment'})}>+</button>
	  <button onClick={() => dispatch({type: 'decrement'})}>-</button>
	  </>
  );
}