ReducerPool.js

export class ReducerPool {
  constructor() {
    this.redusers = [];
  } 
  
  registerReducer(reducer) {
    redusers.push(reducer);
  }
  
  getNewState(state, action) {
    return reducers.reduce((state, reducer) => {
      return reducer.getNewState(state, action);
    }, state);
  }
}


import { BaseReducer } from './BaseReducer'
import { ReducerPool } from './ReducerPool'
import { ADD_TODO } from './constants/TodoActionTypes'

export class AddTodoReducer extends BaseReducer {
  getNewState(state, action) {
    if (action.type === ADD_TODO) {
      return [
        {
          id: state.reduce((maxID, todo) => Math.max(todo.id, maxID),
          completed: false,
          text: action.text
        },
        ...state
      ]
    }
  }
}
                           
ReducerPool.redister(new AddTodoReducer());
          
          
const ACTION_HANDLERS = {
  [ACTION_1]: (state, action) => ...,
  [ACTION_2]: (state, action) => ...,
  [ACTION_3]: (state, action) => ...,
  [ACTION_4]: (state, action) => ...,
  ...
};

const reducer = (state = INITIAL_STATE, action) => {
  const handler = ACTION_HANDLERS[action.type];
  return handler ? handler(state, action) : state;
};