Classy.js is a tiny framework for writing inheritance in JavaScript. It's currently less than 500 bytes. 437, to be exact, even without gzip.

I created Classy.js after visiting John Resig's popular Simple JavaScript Inheritance post in his blog. I sat down and tried to rewrite his implementation in my own version and design. I saw so many tutorials about how to do inheritance in javascript BUT one thing that bothered me a lot is using new during the inheritance implementation.

For example:

function Base(name) {
    this.name = name;
}
	
function Child() {
    Base.apply(this, arguments);
}
	
Child.prototype = new Base();

Frankly, it just feels WRONG. Why instantiate a new object just for my inheritance support? Or rather, I know the reason, but to me it's just a hack; I don't want a hack for a basic feature — and that is why Classy was created.

Highlights:

-> Extremely small and compact. can be copy/paste to any library.

-> Doesn't use new during of implementation of inheritance.

-> Supported by all browsers, old and new.

-> Simple syntax and interface, possibly customizable in terms of reserved key words.

-> Support for class methods

-> Uses prototype technique to reduces over-head of creating an object in JavaScript.

Load the script however you like. For example:

<script type="text/javascript" src="classy-x.y.z.js"></script>

Now you can create the JavaScript classes like this:

var Base = Classy({
    initialize: function() {
        console.log('This is Base.');
    }
});

var Child = Base.extend({
    initialize: function() {
        Child.base(this);
        console.log('This is child');
    }
});

var obj = new Child();

Classy gets create a JavaScript object definition using prototype internally, ready for instantiation.

All the base class starts with Classy object itself. From that point, all the children use extend to extend the Base class.

Note: the extending class needs to pass initialize field, and the first line of the initialize function must call the Base constructor.

Child.base(this);

What about passing arguments to Base constructor? Take a look at the base class method:

<Name of Drive Class>.base(<current object pointer>, <arg1>, <arg2>, ...);

Arguments to initialize can be passed along to the superclass. For example, if the Base constructor accepts 2 arguments, pass them to the subclass and then pass them along to the base class like so:

initialize: function(arg1, arg2, arg3) {
   Child.base(this, arg2, arg3);
   this.value1 = arg1;
}

Classy also supports class methods which you can call directly without instantiation like static methods in JAVA as an example.

Here's an example of singleton implementation with Classy.js:

var Base = Classy({
    initialize: function () {
	console.log('Base instantiated.');
    }
});
    
Classy(Base, {
    getInstance: (function () {
        var instance;
        return function () {
            if (!instance) {
                instance = new Base();
            }
            return instance;
        };
    }()
});

var base = Base.getInstance();

NOTE: I have added test.html which contains full example.

if you have any questions, comments or etc. drop me a message at a[dot]najafizadeh[at]gmail.com.