Ember js observers and computed properties in typescript

How can I define emberjs observers and computed properties using typescript?

I need to write the following code in typescript.

module App {
App.UserController = ember.ObjectController.extend({
    firstName: "John",
    lastName: "Doe",
    fullName: function() {
       return this.get("firstName") + " " + this.get("lastName");
    }.property('model.isCompleted')
});
}