Question

I thought I understood the concept of the JavaScript prototype object, as well as [[proto]] until I saw a few posts regarding class inheritance.

Firstly, “JavaScript OOP – the smart way” at http://amix.dk/blog/viewEntry/19038

See the implementation section:

var parent = new this('no_init');

And also “Simple JavaScript Inheritance” on John Resig’s great blog.

var prototype = new this();

What does new this(); actually mean?

This statement makes no sense to me because my understand has been that this points to an object and not a constructor function. I’ve also tried testing statements in Firebug to figure this one out and all I receive is syntax errors.

My head has gone off into a complete spin.

Could someone please explain this in detail?

Answer 1

AJS.Class effectively* translates this:

var Person = new AJS.Class({
    init: function(name) {
        this.name = name;
        Person.count++;
    },
    getName: function() {
        return this.name;
    }
});
Person.count = 0;

into this:

var Person = function (name) {
    this.name = name;
    Person.count++;
};

Person.prototype = {
    getName: function() {
        return this.name;
    }
};

Person.extend = AJS.Class.prototype.extend;
Person.implement = AJS.Class.prototype.implement;

Person.count = 0;

Therefore, in this case, this in AJS.Class.prototype.extend refers to Person, because:

Person.extend(...);
// is the same as
Person.extend.call(Person, ...);
// is the same as
AJS.Class.prototype.extend.call(Person, ...);

* There are a lot of cases I don’t go over; this rewrite is for simplicity in understanding the problem.