Edit in JSFiddle

        var Class = (function(){
            
            // private valiable
            var privates = {
                names: {}
            };
                    
            var _class = function(){
                
                this.id = 'mohwa';
                this.key = String(new Date().getTime());
                
                return this;
            }
            
            _class.fn = _class.prototype = {
                getName: function(){
                    return privates['names'[this.key]];
                },
                setName: function(name){
                    privates['names'[this.key]] = name;
                    return this;
                }
            }
            
            return _class;
        })();
        
        alert(new Class().setName('전성균').getName());
        
        alert(new Class().names);