Redux 减速器初始化相同的状态键

我正在搞乱github 上的“最简单的 Redux 示例” https://github.com/jackielii/simplest-redux-example我添加了第二个减少 state.count 的减速器。如果我在 switch case 语句中有增量和减量缩减器，它就可以正常工作。我想要执行的练习是将减速器分成尽可能多的模块化部分。此代码抛出一个错误，指出计数未定义。

import React from 'react';
import { createStore, combineReducers } from 'redux';
import { Provider, connect } from 'react-redux';

// React component
class Counter extends React.Component {
  render(){
    const { value, onIncreaseClick, onDecreaseClick } = this.props;
    return (
      <div>
        <span>{value}</span>
        <button onClick={onIncreaseClick}>Increase</button>
        <button onClick={onDecreaseClick}>Decrease</button>
      </div>
    );
  }
}

// Action:
const increaseAction = {type: 'increase'};
const decreaseAction = {type: 'decrease'};

// Reducer:
function counter(state, action) {
  let count = state.count;
  switch(action.type){
    case 'increase':
      return {count: count+1};
    default:
      return state;
  }
}
function decrementer(state, action) {
  let count = state.count;
  switch(action.type){
    case 'decrease':
      return {count: count -1};
    default:
      return state;
  }
}
const rootReducer = combineReducers({
  counter,
  decrementer
})

// Store:
let store = createStore(rootReducer, {count: 0});

// Map Redux state to component props
function mapStateToProps(state)  {
  console.log("mapStatetoProps heyyyy");
  return {
    value: state.count
  };
}

// Map Redux actions to component props
function mapDispatchToProps(dispatch) {
  console.log("mapDispatchtoProps heyyyy");
  return {
    onIncreaseClick: () => dispatch(increaseAction),
    onDecreaseClick: () => dispatch(decreaseAction)
  };
}

// Connected Component:
let App = connect(
  mapStateToProps,
  mapDispatchToProps
)(Counter);

React.render(
  <Provider store={store}>
    {() => <App />}
  </Provider>,
  document.getElementById('root')
);

减速器传递给combineReducers变得不同pieces状态对象的。

生成的减速器调用每个子减速器，并将其结果收集到单个状态对象中。状态对象的形状与传递的键相匹配reducers.

（强调我的）

所以，内部状态对象看起来像

{
  counter: result of passing `state.counter` into counter reducer
  decrementer: result of passing `state.decrementer` into decrementer reducer
}

这类似于在 Flux 应用程序中拥有单独的商店，其中每个商店都运行自己的全局应用程序状态的“部分”。

因为您实际上希望这两个减速器在same状态对象的一部分，你实际上想要的东西更像减少减速器 https://github.com/acdlite/reduce-reducers，尽管自己实现起来非常容易——只需将状态依次传递到每个减速器中，用来自每个减速器的新状态来减少初始状态。

其实就这么简单，实现就几行：

export default function reduceReducers(...reducers) {
  return (previous, current) =>
    reducers.reduce(
      (p, r) => r(p, current),
      previous
    );
}

和你的rootReducer将会

const rootReducer = reduceReducers(counter, decrementer);