ReduxReducer

A Reducer is a pure function that takes the state of an application and action as arguments and returns a new state.

const initialState = {};
const action = {
  type: 'ADD_TO_CART',
  payload: {
    product: 'margarine',
    quantity: 4
  }
}
const cartReducer = (state = initialState, action) => {
  // Do something here
}

combineReducers的简单实现

const combineReducers = reducers => {
    return (state = {}, action) => {
        return Object.keys(reducers).reduce((nextState, key) => {
            nextState[key] = reducers[key](state[key], action);
            return nextState;
        },{});
    };
};