I can't receive data from custom module in node.js -

i wrote module called accountmanager.js

var sqlite3 = require('sqlite3');  var db = new sqlite3.database("./users.db");  exports.userexists = function userexists(nickname) {     var stmt = 'select * users login="' + nickname + '"';     db.each(stmt,function(err,row) {         if(row) {             if(row.login==nickname) return true;             else return false;         }     }); } 

in main app.js file i've got

var accountmanager = require('./lib/accountmanager'); console.log(accountmanager.userexists('user1')); 

this app says 'undefined' in console... checked module working fine, guess it's problem callback? please, give me help, don't understand wrong code...

you need understand how asynchronous functions , callbacks work.

basically cannot return inside callback need invoke callback pass userexists.

var sqlite3 = require('sqlite3'); var db = new sqlite3.database("./users.db");  exports.userexists = function userexists(nickname, cb) {     var stmt = 'select * users login="' + nickname + '"';     db.each(stmt,function(err,row) {         if(row) {             cb(row.login == nickname);         }     }); } 

to use it:

accountmanager.userexists('user1', function(found) {     console.log(found); }); 

besides that, code has gaping sql injection hole , might not intend do. here's fixed version of userexists function:

exports.userexists = function userexists(nickname, cb) {     var stmt = 'select count(*) cnt users login = ?';     db.get(stmt, nickname, function(err, row) {         cb(row.cnt > 0);     }); }; 

why better?

1. you not interpolate value in sql string (which bad, have escape stuff avoid sql injection). passing separately cleaner , better
2. you want know if user exists. retrieve count (which 1 row). if it's not 0 user exists.
3. now callback invoked. in first example more closely based on code invoked in case user has been found - not wanted.