Ways to compose objects

• class / new

• Object.create()

• Object.assign()

Task:

• Create Dog and Cat instances
• Both animals have a name
• Both animals can walk()
• Dogs can bark()
• Cats can knockStuffOffCounter()

Object.create()

const animalProto = {
  init(name) {
    this.name = name;
  },
  walk() {
    console.log(`${this.name} walked over there`);
  }
};

const dogProto = Object.create(animalProto);
Object.assign(dogProto, {
  bark() {
    console.log(`${this.name} said "woof"`);
  }
});

const catProto = Object.create(animalProto);
Object.assign(catProto, {
  knockStuffOffCounter() {
    console.log(`${this.name} knocked a full glass of water over`);
  }
});

Object.create() cont.

function createDog(name) {
  const instance = Object.create(dogProto);
  instance.init(name);
  return instance;
}

function createCat(name) {
  const instance = Object.create(catProto);
  instance.init(name);
  return instance;
}

animalProto

dogProto

createDog('[name]')

[[Prototype]]

[[Prototype]]

Object.assign()

const animal = {
  init(name) {
    this.name = name;
  },
  walk() {
    // ...
  }
};

const dog = {
  bark() {
    // ...
  }
};

const cat = {
  knockStuffOffCounter() {
    // ...
  }
};

Object.assign() cont.

function createDog(name) {
  const instance = Object.assign({}, dog, animal);
  instance.init(name);
  return instance;
}

function createCat(name) {
  const instance = Object.assign({}, cat, animal);
  instance.init(name);
  return instance;
}

Object.assign() alt.

const walker = {
  walk() {
    // ...
  }
};

const nameable = {
  init(name) {
    this.name = name;
  }
};

const barker = {
  bark() {
    // ...
  }
};

const messCreator = {
  knockStuffOffCounter() {
    // ...
  }
};

Object.assign() alt. cont.

function createDog(name) {
  const instance = Object.assign({}, nameable, walker, barker);
  instance.init(name);
  return instance;
}

function createCat(name) {
  const instance = Object.assign({}, nameable, walker, messCreator);
  instance.init(name);
  return instance;
}