var mysql = require("mysql");var Event = require("events").EventEmitter;var user = "lubingjie";var pass = "123456";var db = mysql.createConnection({host:"localhost",user:"root",password:"",database:"test"});//链接数据库var ev = new Event();//实例化eventsev.on("error",function(err){//添加监听err的事件  统一的错误处理函数    console.log("数据库出错了！");});function query(sql,fn){//执行函数    db.query(sql,function(err,data){        if(err)            ev.emit("err",err);//执行监听的事件        else{            fn(data);        }    });}query("select * from user where username=‘"+user+"‘ and pass=‘"+pass+"‘",function(data){    if(data.length==0){        query("insert into user values(‘"+user+"‘,‘"+pass+"‘)",function(data){            console.log("完成！");        });    }else{        console.log("用户名已经存在！");    }});