'This' is not the same in constructor and inherited constructor

Question

I have this simple inheritance pattern:

function Emitter() {
    this.dis1 = this;
};

function Person() {
    this.dis2 = this;
};
Person.prototype = new Emitter();
var p1 = new Person();
var p2 = new Person();

console.log(p1.dis1 === p2.dis1); //true - why?
console.log(p1.dis2 === p2.dis2); //false

Why are dis1 separate objects the same? Is there a workaround for this?

Answer 1

A note on how newoperator works :

Foo = function(){};
Foo.prototype;

var bar = new Foo();

What happens on the last line, a new object is created that inherits from Foo.prototype, and then the code in the function Foois executed with thisthis new object. Then the line is initialized with this new object.

---

There are several drawbacks to your inheritance model, and you have discovered one of them. All the flaws are related to this line of code:

Person.prototype = new Emitter();

, , Person, - Emitter ( Emitter, ).

p1.dist1 dist1 . p1, , dist1, . p1.[[Prototype]], Person.prototype, dist1, Person.prototype ( Emitter, ).

p1.dist , p1 p1.

p2, p2.dist1, Emitter, p2.dist2 p2.

---

:

function Emitter() {
    this.dis1 = this;
};

function Person() {
    Emitter.call(this); // calls the parent constructor.
    this.dis2 = this;
};
Person.prototype = Object.create(Emitter.prototype); // you don't even use this line

var p1 = new Person();
var p2 = new Person();

p1.dist1 === p1 p1.dist2 === p1, p2.dist1 === p2 p2.dist2 === p2. , , Emitter , Person. , Emitter this.dis1 = this, this p1 p2.

, , :

• , Emitter.prottoype, p1 p2
• p1 instanceof Emitter .

, MDN.

Answer 2

dis1 .

p1 p2, , , new Emitter(). , .

JavaScript , , Java. , Java ++ JavaScript: .

, Emitter Person, ( initialize, ).

:

function Emitter() {
}
Emitter.prototype.register = function(thing){
  if (!this.listeners) {
      this.listeners = []; 
  }
  this.listeners.push(thing);
}

function Person() {
}
Person.prototype = new Emitter();

, , , , , .

Answer 3

dystroy, dis1 . dis1 Person s, .

function Emitter() {
    this.dis1 = this;
};

function Person() {
    Emitter.call(this);
    this.dis2 = this;
};
Person.prototype = Object.create(Emitter.prototype);
var p1 = new Person();
var p2 = new Person();

console.log(p1.dis1 === p2.dis1); //false
console.log(p1.dis2 === p2.dis2); //false

, Emitter Person, this . Person , () Person, () Emitter :

{
    dis1: Person,
    dis2: Person
}

Object.create . , Emitter , , , dis1, -.