How does JavaScript maintain the prototype reference?

Question

Looking at the answer to (How does the prototype chain work?) I can see that there is an inheritance chain. What is happening behind the scenes?

As far as I can tell the prototype property stores a reference to the prototype object? Why does that object not include the prototype's prototype and how is it maintaining that reference instead?

var Parent = function() {
	this.name = 'Parent';
}

Parent.prototype.sayHi = function() {
	console.log('hi');
}

var Child = function() {
	this.name = "Child";
}

Child.prototype = new Parent();

console.log(Parent.prototype); // { sayHi: [Function] }
console.log(Child.prototype); // { name: 'Parent' }
console.log(Child.prototype.prototype); // undefined

=============== Answer from below ===============

console.log(Parent.prototype); // { sayHi: [Function] }
console.log(Child.prototype); // { name: 'Parent' }
console.log(Child.prototype.__proto__); // { sayHi: [Function] }

That's not a correct output from your code. Create an inline snippet. — Amit
– Amit, Commented Jul 29, 2015 at 19:28
it does "include the prototype's prototype", if you setup such a relationship. in the code shown, there's no tying of Child to Parent, so it would be surprising if they were connected for you... — dandavis
– dandavis, Commented Jul 29, 2015 at 19:32

Alexander O'Mara · Accepted Answer · 2015-07-29 19:46:43Z

3

Why does that object not include the prototype's prototype and how is it maintaining that reference instead?

Because in your example, the prototype of Child is also an instance of Parent, not another constructor. The prototype is a property of the constructor, not a property of each individual instance.

There is another property that does this for each instance, the __proto__ property, but it has almost no sane uses. The ES6 specification also only requires the feature be implemented in web browser, and not necessarily other JavaScript environments.

edited Jul 29, 2015 at 19:46

answered Jul 29, 2015 at 19:40

Alexander O'Mara

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