class.md

Class / Prototypal inheritance

In Js, all functions by default get a public property on them called prototype.

function Foo(){
  // ...
}

Foo.prototype; // { }

Each object created from called new Foo() will end up [[Prototype]]-linked to this object.

function Foo(){

}

var a = new Foo();

Object.getPrototypeOf(a) === Foo.prototype; // true

When a is created by calling new Foo(), a gets an internal [[Prototype]] link to the object that Foo.prototype is pointing at.

In JS, there are no copies of a class being made. You can't create multiple instances of a class, you can create multiple objects that [[Prototype]] link to a common object.

The objects don't end up totally separate and disconnected to each other, but rather, linked.

In JS, we don't make copies from one object ("class") to another ("instance"). We make links between objects.

This mechanism is called Prototypal inheritance.

Constructors

Take the following example:

function Foo(){
  console.log("hello");
}

var a = new Foo(); // hello;

a; // {}

Foo is just a normal function, but when called with new, it constructs an object which we assign to a. The call was a constructor call, but Foo is not a constructor.

Functions aren't constructors but function calls are "constructor calls" if new is used.

Object.create()

Using Object.create() creates a new object.