this.todos = this.todos.map<ITodo>((todo: ITodo) => {
   return todo !== todoToToggle ?
     todo :
     Utils.extend(
       {}, todo, { completed: !todo.completed }
     )
 })

  public addTodo(title: string) {
    var d = new Date();
    var date = [d.getFullYear(), d.getMonth() + 1, d.getDate()]

    this.todos = this.todos.concat({
      id: Utils.uuid(),
      title: title,
      completed: false,
      date: { 'year': date[0], 'month': date[1], 'date': date[2] }
    })
    this.inform()
  }

 constructor(key) {
   this.key = key;
   this.todos = Utils.store(key);
   this.onChanges = [];
 }

 public inform() {
   Utils.store(this.key, this.todos)
   this.onChanges.forEach((cb) => cb())
 }