Resig's Class.extend minified

Class.js

var Class = function(){var d=!1,g=/xyz/.test(function(){})?/\b_super\b/:/.*/;this.Class=function(){};Class.extend=function(b){function c(){!d&&this.init&&this.init.apply(this,arguments)}var e=this.prototype;d=!0;var f=new this;d=!1;for(var a in b)f[a]="function"==typeof b[a]&&"function"==typeof e[a]&&g.test(b[a])?function(a,b){return function(){var c=this._super;this._super=e[a];var d=b.apply(this,arguments);this._super=c;return d}}(a,b[a]):b[a];c.prototype=f;c.prototype.constructor=c;c.extend=arguments.callee; return c};return Class}();

Usage.js

var Foo = Class.extend({
    init: function() {
        this.foo = "bar";
    }
});

var FooTwo = Foo.extend({
    init: function() {
        this._super();
        this.foo2 = "bar2";
    }
});

var f = new Foo();
var f2 = new FooTwo();

console.log( f.foo );
console.log( f.foo2 );

console.log( f2.foo );
console.log( f2.foo2 );