tasks.js

Todos.tasksController = SC.ArrayController.create({

  countSummary: function() {
    var length = this.get('length');
    if(length == 0)
      return 'No Tasks';
    else
      return length == 1 ? '1 Task' : "%@ Tasks".fmt(length);
  }.property('length').cacheable(),

  addTask: function() {
    Todos.store.createRecord(Todos.Task, { "description": "New Task", "isDone": false }); // ADDED THIS
  }
});