Discussion on: Looking at the Prototype

[peerreynders]

prototype is the property you set on a constructor function - any objects created via new will have that object as their prototype.

// Constructor function
function Car(make, model) {
  if (typeof make === 'string') this.make = make;
  if (typeof model === 'string') this.model = model;
}

function getCarInfo() {
  return `${this.make} ${this.model}`;
}

Car.prototype = {
  make: 'Default',
  model: 'Default',
  getCarInfo,
};

const volvo = new Car('Volvo', 'S80');

console.assert(volvo.getCarInfo() === 'Volvo S80');

While the actual object prototype link is an internal property, i.e. it's implementation dependent to allow for optimization, Firefox's JavaScript engine SpiderMonkey exposed it with __proto__ which was soon copied by other browsers.

ES2015:
1.) deprecates __proto__
2.) turned __proto__ into a getter/setter.

__proto__ in ECMAScript 6

Now if you want to get the prototype of an object use Object.getPrototypeOf() and you can create an object with a prototype with Object.create()

function getCarInfo() {
  return `${this.make} ${this.model}`;
}

const car = {
  make: 'Default',
  model: 'Default',
  getCarInfo,
};

const volvo = Object.create(car);
volvo.make = 'Volvo';
volvo.model = 'S80';

console.assert(volvo.getCarInfo() === 'Volvo S80');

JavaScript's prototypal inheritance is based on Self.