extend is actually returning a new class by Metadata.createClass

create prototype chain

fnClass.prototype = jQuery.sap.newObject(fnBaseClass.prototype);

fnClass.prototype.constructor = fnClass;

Make the class visible as JS Object: jQuery.sap.setObject(sClassName, fnClass);

fnClass.getMetadata = fnClass.prototype.getMetadata = jQuery.sap.getter(oMetadata);