node.js - NodeJS : can not emit event "Object ...{} has no method 'emit' -

i followed few nodejs tutorials ang got through simple rest webservice. webservices listens /api/accounts email , password, proceeds lookup in cassandra cluster. use eventemitter avoid callback hell. works fine until emit('success') attempted :

events.js:72         throw er; // unhandled 'error' event               ^ typeerror: object select * accounts email_accounts=?,test@gmail.com,77ddcc8d868e1532f86f0e25f35d43e5,function _checkpassword(error, response) {         var rows=response.rows;         if (_checkforerrors(error, rows , 'password')) {             return false;         } else {             if ( rows.length == 1 ) {                 console.log('got user profile password_accounts ' + rows[0].pwd_accounts);                 this.emit('success', rows[0] );             }         }     } has no method 'emit'     @ array._checkpassword (/home/scoulibaly/node/login.js:33:10)     @ /home/scoulibaly/node/node_modules/node-cassandra-cql/index.js:220:16     @ connection.handleresult (/home/scoulibaly/node/node_modules/node-cassandra-cql/lib/connection.js:308:3)     @ resultemitter.eventemitter.emit (events.js:106:17)     @ resultemitter.bufferandemit (/home/scoulibaly/node/node_modules/node-cassandra-cql/lib/streams.js:456:10)     @ resultemitter.each (/home/scoulibaly/node/node_modules/node-cassandra-cql/lib/streams.js:440:17)     @ resultemitter._write (/home/scoulibaly/node/node_modules/node-cassandra-cql/lib/streams.js:413:10)     @ dowrite (_stream_writable.js:223:10)     @ writeorbuffer (_stream_writable.js:213:5)     @ resultemitter.writable.write (_stream_writable.js:180:11) 

my main server.js. use express , router() setup routes :

// server.js  // base setup // =============================================================================  // call packages need var express    = require('express');        // call express var app        = express();                 // define our app using express var bodyparser = require('body-parser');   var login   = require('./login');  // configure app use bodyparser() // let data post app.use(bodyparser.urlencoded({ extended: true })); app.use(bodyparser.json());  var port = process.env.port || 8080;        // set our port  // routes our api // ============================================================================= var router = express.router();              // instance of express router  // middleware use requests router.use(function(req, res, next) {     // logging     console.log('something happening.');     next(); // make sure go next routes , don't stop here });   router.route('/accounts')     // account id (accessed @ http://localhost:8080/api/accounts/:account_id)     .get(function(req, res) {        var login = new login(req.query.email, req.query.password);         login.on('error', function (error) {             res.writehead(500);             res.end();         });         login.on('failure', function (reason) {             if (reason == 'email') {                 res.end('wrong email!');             } else if (reason == 'password') {                 res.end('wrong password!');             }         });         login.on('success', function (data) {             res.json(data);         });         login.perform();     });   // test route make sure working (accessed @ http://localhost:8080/api) router.get('/', function(req, res) {     res.json({ message: 'hooray! welcome our api!' });    });  // more routes our api happen here  // register our routes ------------------------------- // of our routes prefixed /api app.use('/api', router);  // start server // ============================================================================= app.listen(port); console.log('magic happens on port ' + port); 

my login.js extends eventemitter :

// login.js  var util        = require('util'); var eventemitter = require('events').eventemitter; var cql        = require('node-cassandra-cql');   function login(email,password) {     // error checking     function _checkforerrors(error, rows, reason) {         if (error) {             console.log('emit err');             this.emit('error', error);             return true;         }          if (rows.length < 1) {                         console.log('emit fail');             this.emit('failure', reason);             return true;         }          return false;     }      // check {email,pwd}     function _checkpassword(error, response) {         var rows=response.rows;         if (_checkforerrors(error, rows , 'password')) {             return false;         } else {             if ( rows.length == 1 ) {                 console.log('got user profile password_accounts ' + rows[0].pwd_accounts);                 this.emit('success', rows[0] );             }         }     }      function perform() {         var client = new cql.client({hosts: ['localhost', 'localhost'], keyspace: 'node'});         client.execute('select * accounts email_accounts=?', [ email , password ], _checkpassword );     }      this.perform = perform; }   util.inherits(login, eventemitter); module.exports = login; 

it looks 'this' in this.emit() lines refer cql object. in understanding, cql drivers calls callback whenever data ready, 'this' object not login object anymore. wrong ? how can have emit() work ?

thank you

near top of login object definition, create handle this via:

var _this = this; 

then use _this instead of this when calling emit method. _checkpassword said close on _this (which can't on this).

the this keyword special snowflake dynamically bound when enclosing function invoked; if pass function refers this off other functions, make sure this think is. :)