oop - Why my extend() method in Javascript don't work for 3 and more objects? -

i have 3 object.

netbuilder numbering numberingmethoddefault

and have extend method.

extend: function (child, parent) {   var f = function () {};   f.prototype = parent.prototype;   child.prototype = new f();   child.prototype.constructor = child;   child.superclass = parent.prototype;   this.mixin(child, parent); }, /**   * @param {type} dst  * @param {type} src  * @returns {undefined}  */ mixin: function (dst, src) {   var tobj = {};   (var x in src) {     if ((typeof tobj[x] == "undefined") || (tobj[x] != src[x])) {       dst[x] = src[x];     }   }   if (document.all && !document.isopera) {     var p = src.tostring;     if (typeof p == "function" && p != dst.tostring && p != tobj.tostring &&       p != "\nfunction tostring() {\n    [native code]\n}\n") {       dst.tostring = src.tostring;     }   } } 

than try numbering extends netbuilder , numberingmethoddefault extends numbering.

ooputility.extend(numbering, netbuilder); ooputility.extend(numberingmethoddefault, numbering); 

and call superclassses

numbering.superclass.constructor.call(this, arguments); numberingmethoddefault.superclass.constructor.call(this, arguments); 

numbering has method setnumber(). have access in numbering netbuilder methods, in numberingmethoddefault can't execute method setnumber() numbering.

uncaught typeerror: object #<numberingmethoddefault> has no method 'setnumber' 

than console.log() superclass numberingmethoddefault

console.log(numberingmethoddefault.superclass); //and netbuilder, not numbering! о_О 

how can make work. need extend 3 or more objects!

this because call mixin manually copies properties 1 object other, , overwriting .superclass assignment. if you're emulating class inheritance won't need mixins in way, remove code altogether , shouldn't have problem.