Javascript - KineticJS create own class -

how create new class based on kineticjs sprite class. i'm trying this:

(function() {     kinetic.mycircle = function(config) {         this._initmycircle(config);     };      kinetic.mycircle.prototype = {         _initmycircle: function(config) {             kinetic.circle.call(this, config);             },         myfunc : function(){         }     };    kinetic.global.extend(kinetic.mycircle, kinetic.circle); })();   

but error: typeerror: kinetic.global.extend not function

i believe looking for:

kinetic.util.extend(kinetic.mycircle, kinetic.circle); 

this works in kineticjs 4.5.1