javascript - How to callback function from another file in nodejs? -

im starting work async programming, im making nodejs application, i´ve slice code in files: index.js, ctluser.js, dao.js etc... .. index.js main file requires ctluser , ctluser require dao.js... dao connect database , execute queries...

abstracting, structure this...

index.js

var ctluser =  require('./ctluser.js'); var username = ctluser.getusername('1'); console.log("return ctluser" + username); 

ctluser.js

var dao = require('./dao.js'); var getusername = function(id){     var username = dao.executequery("select username tbusers id = " + id );     console.log(return dao = username);     return username; } 

dao.js here fine...

var mysql      = require('mysql');  var executequery = function(query) {             var connection = mysql.createconnection({             host        : server,             user        : user,             password    : password,             database    : database         });         connection.connect();         connection.query(query, function(err, rows, fields) {             if (err) throw err;             connection.end();             console.log("here in dao: " + rows[0].username);             return rows[0].username;         });     }; 

the output of $ node index.js is:

return of ctluser: undefined return of dao: undefined here in dao: filipe tagliacozzi 

im abstracting module exports everithing works fine fixed variables, database response dont..how implement callbacks in structure take username index.js?

change executequery function in dao.js module use callback:

var executequery = function(query,callback) {             var connection = mysql.createconnection({             host        : server,             user        : user,             password    : password,             database    : database         });         connection.connect();         connection.query(query, function(err, rows, fields) {             if (err) throw err;             connection.end();             console.log("here in dao: " + rows[0].username);             callback(rows[0].username);         });     }; 

chain callback through getusername function in ctluser.js:

    var getusername = function(id,callback){         dao.executequery("select username tbusers id = " + id ,function(username){            console.log("return dao =" ,username);            callback(username);         });            } 

then consume in index.js so:

var ctluser =  require('./ctluser.js'); ctluser.getusername('1',function(username){     console.log("return ctluser" + username); });