cocos2dx 3.3 quick lua 实现返回键退出程序

<span style="font-size:18px;">    local layer = display.newLayer()    
    self:addChild(layer,-10)  
    layer:setKeypadEnabled(true)  
    layer:addNodeEventListener(cc.KEYPAD_EVENT,function (event)  
        if event.key == "back" then  --返回键
            print("back")  --弹出一个对话框，点击yes退出程序
            device.showAlert("Confirm Exit","Are you sure exit game ?",{"YES","NO"},function (event)

                if event.buttonIndex == 1 then  
                    cc.Director:getInstance():endToLua()
                else  
                    device.cancelAlert()  --取消对话框 
                end  
            end)           
        elseif event.key == "menu" then  --菜单键
            print("menu")               
        end        
    end) </span>