Immutable.Record + React + Redux = ❤ - 3

reducers-tasks.js

import { RECEIVED_ENTITIES, DELETE_TASK, TOGGLE_TASK_DONE } from 'constants/ActionsTypes';
import Task from 'models/Task';
import TaskMap from 'models/TaskMap';

const initialState = new TaskMap();

const mergeEntities = (state, newTasks) =>
  state.merge(newTasks.map((task) => new Task(task)))

export default (state = initialState, action) => 
  switch(action.type) {
    // Received tasks data from an external API
    case RECEIVED_ENTITIES:
      if (!action.entities.tasks) { return state }
      return mergeEntities(state, Immutable.fromJS(action.entities.tasks));
    
    // Handles some UI actions
    case DELETE_TASK:
      return state.remove(action.taskId);

    case TOGGLE_TASK_DONE:
      return state.update(action.taskId, (task) =>  task.set('done', !task.get('done')));

  }
}