class OrdinaryUser{
	buy(){
		console.log('普通用户购买')
	}
};
class MemberUser{
	buy(){
		console.log('会员用户购买')
	}
};
class VipUser{
	buy(){
		console.log('VIP用户购买')
	}
}
const u1=new OrdinaryUser();
const u2=new MemberUser();
const u3=new VipUser();
u1.buy();
u2.buy();
u3.buy();