Ember.js: Unexpected token

I am learning ember.js and I am following this tutorial:

https://youtu.be/owDmPTSJkrg?t=1194

I am writing a controller for a form:

import Controller from '@ember/controller';

export default class TasksNewController extends Controller {
    actions:{
        addTask: function() {
            var title = $this.get('title');
            alert(title);
        }
    }
}

I get this error:

Build Error (broccoli-persistent-filter:Babel > [Babel: emtasks]) in emtasks/controllers/tasks/new.js

/Users/.../Desktop/emtasks/emtasks/controllers/tasks/new.js: Unexpected token (4:11)

  2 | 
  3 | export default class TasksNewController extends Controller {
> 4 |     actions:{
    |            ^
  5 |         addTask: function() {
  6 |             var title = $this.get('title');
  7 |             alert(title);

Thank you for any suggestions