Simple redux todo implementation with mocha tests

redux-mocha.js

var expect = require('chai').expect;

// store
const createStore = (reducer) => {
  let listeners = [];
  let state;
  
  const getState = () => state;
  
  const subscribe = (listener) => {
    listeners.push(listener);
    return () => {
       listeners = listeners.filter(l => l !== listener);
    };
  };
  
  const dispatch = (action) => {
     state = reducer(state, action);
    listeners.forEach(listener => listener());
  };
  
  dispatch({});

  return { getState, subscribe, dispatch };
};


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

// the reducers
const todo = (state, action) => {
  switch(action.type) {
    case 'ADD_TODO':
      return {
        id: action.id,
        text: action.text,
        completed: false
      };
    case 'TOGGLE_TODO':
      if(state.id !== action.id) {
        return state;
      }
      
      return Object.assign({}, state, {
        completed: !state.completed
      });
    default:
      return state;
  }
}

const todos = (state = [], action) => {
  switch(action.type) {
    case 'ADD_TODO':
      return [
        ...state,
        todo(undefined, action)
      ];
    case 'TOGGLE_TODO':
      return state.map(s => todo(s, action));
    default:
      return state;
  }
};

const createActionCreator = (store) => {
  let countTodo = 0;
  const addTodo = (text) => {
    // async stuff here... on success callback dispatch...
    store.dispatch({
      type: 'ADD_TODO',
      id: ++countTodo,
      text: text
    });      
  };
  
  const toggleTodo = (id) => {
    store.dispatch({
      type: 'TOGGLE_TODO',
      id: id
    });
  };
  
  return {addTodo, toggleTodo};
}



var todoApp = combineReducers({todos});


describe('todolist', () => {
	let store;
	let actionCreator;
	beforeEach(() => {
		store = createStore(todoApp);
		actionCreator = createActionCreator(store);
	});

	it('is empty initially', () => {
		expect(store.getState().todos).to.deep.equal([]);
	});

	describe('Scenario: Adding a new todo to the todolist', () => {
			
		it('rocks', () => {
			actionCreator.addTodo('Blaaa');
			var expectedState = [
				{
					id: 1,
					text: 'Blaaa',
					completed: false
				}
			];
			expect(store.getState().todos).to.deep.equal(expectedState);
		});
	});
});