Function

extend (mixins, arguments) public

Module:	@ember/object

Defined in packages/ember-runtime/lib/system/core_object.js:560

mixins

Mixin

One or more Mixin classes

arguments

Object

Object containing values to use within the new class

Creates a new subclass.

const Person = Ember.Object.extend({
  say(thing) {
    alert(thing);
   }
});

This defines a new subclass of Ember.Object: Person. It contains one method: say().

You can also create a subclass from any existing class by calling its extend() method. For example, you might want to create a subclass of Ember's built-in Ember.Component class:

const PersonComponent = Ember.Component.extend({
  tagName: 'li',
  classNameBindings: ['isAdministrator']
});

When defining a subclass, you can override methods but still access the implementation of your parent class by calling the special _super() method:

const Person = Ember.Object.extend({
  say(thing) {
    let name = this.get('name');
    alert(`${name} says: ${thing}`);
  }
});

const Soldier = Person.extend({
  say(thing) {
    this._super(`${thing}, sir!`);
  },
  march(numberOfHours) {
    alert(`${this.get('name')} marches for ${numberOfHours} hours.`);
  }
});

let yehuda = Soldier.create({
  name: 'Yehuda Katz'
});

yehuda.say('Yes');  // alerts "Yehuda Katz says: Yes, sir!"

The create() on line #17 creates an instance of the Soldier class. The extend() on line #8 creates a subclass of Person. Any instance of the Person class will not have the march() method.

You can also pass Mixin classes to add additional properties to the subclass.

const Person = Ember.Object.extend({
  say(thing) {
    alert(`${this.get('name')} says: ${thing}`);
  }
});

const SingingMixin = Mixin.create({
  sing(thing){
    alert(`${this.get('name')} sings: la la la ${thing}`);
  }
});

const BroadwayStar = Person.extend(SingingMixin, {
  dance() {
    alert(`${this.get('name')} dances: tap tap tap tap `);
  }
});

The BroadwayStar class contains three methods: say(), sing(), and dance().