A gist showcasing object composition, using Object.Assign

ObjectAssignComposition.js

//=============================================================================
// Object.Assign                                                             
//=============================================================================


class Robot {
  constructor(name) {
    this._name = name;
  }

  speak() {
    console.log(`I am the robot ${this._name}.`);
  }
}

class Dog {
  constructor(name) {
    this._name = name;
  }

  bark() {
    console.log(`${this._name}: Bowowow`);
  }
} 

class RobotDog {
  constructor(name, dog, robot) {
    //We pass a dog and a robot into the new robot dog to use the methods attach to those instances.
    Object.assign(this, {dog: dog}, {robot: robot});
    this._name = name;
    console.log(this); //RobotDog {dog: Dog, robot: Robot, _name: "CarlBen"}
  }

  bark() {
    this.dog.bark();
  }

  speak() {
    this.robot.speak();
  }
}

var robot = new Robot('Carl');
robot.speak();// I am the robot Carl.

var dog = new Dog("Ben");
dog.bark(); // Ben: Bowowow

var roboDog = new RobotDog('CarlBen', dog, robot);
roboDog.bark(); // Ben: Bowowow
roboDog.speak(); // I am a robot Carl.