用闭包实现命令模式

var Tv = {
    open: function(){
        console.log('打开电视机');
    },
    close: function(){
        console.log('关上电视机');
    },
};

var OpenTvCommand = function(receiver){
    this.receiver = receiver;
};

OpenTvCommand.prototype.execute = function(){
    this.receiver.open();  // 执行命令，打开电视机
};

OpenTvCommand.prototype.undo = function(){
    this.receiver.close();  // 撤销命令，关闭电视机
};

command = new OpenTvCommand(Tv);
command.execute()  // 输出：打开电视机
command.undo()  // 输出：关上电视机