var member = {
                 firstName:"XYZ",lastName:"zzz",get fullName(){ return (this.firstName + ' ' + this.lastName); }
              }

我甚至可以像这样在飞行中添加更多的属性

member.isGuest = true;

但是有什么办法可以将getter添加到已经存在的对象中吗？这样的东西

member.isGuest = get isGuest(){ return this.firstName=='Guest';}