Redux 2

JS.js

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 {
        id: state.id,
        text: state.text,
        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(t => todo(t, action));
    default:
      return state;
  }
};

const { createStore }  = Redux;
const store = createStore(todos);

store.dispatch({
  type: 'ADD_TODO',
  id: 0,
  text: 'Go shopping'
});

store.dispatch({
  type: 'ADD_TODO',
  id: 1,
  text: 'Go shopping'
});

store.dispatch({
  type: 'TOGGLE_TODO',
  id: 1
});

console.log(store.getState());