Prototypes and Constructors

The prototype property is created internally once you declare a function like this:

function Person(firstname, lastname) {
    this.firstname = firstname;
    this.lastname = lastname;
}

Let's add a function to our prototype:

Person.prototype.sayHello = function() {
    console.log('Hello ' + this.firstname + ' ' + this.lastname);
}

Now, Everything you put on the Prototype can be accessed by any instances created using new Person, which means we can do something like this:

var p1 = new Person('John', 'Doe');
var p2 = new Person('Jane', 'Doe');

p1.sayHello();

Every instance created from Person will have a proto property which will point to the Person.prototype. This is what's known as Prototypal inheritance.

So to sum it up;

• An instance created from Person will have a proto property pointing to Person.prototype.

• Person is a Function Object and it will have a proto property that points to the Function.prototype.

• The Function.prototype will again have a proto pointing to the Object.prototype.

• The Object.prototype is the absolute top level.

This picture explains is very well

What I mean by 'absolute top level', is when you follow the prototype chain to the top, it stops at the Object.prototype.

The Object.prototype's proto is null. Look at the link I included in my answer.

No problem - This is a really confusing topic.