Node JS event not firing

Question

I am trying to make an event fire in my node JS code but cannot work out why it isn't.

I have a module as follows:

var zookeeper = require('node-zookeeper-client'),
    events = require('events'),
    util = require('util');
var client;

var KafkaZookeeperMonitor = function(){
    events.EventEmitter.call(this);  
}

util.inherits(KafkaZookeeperMonitor, events.EventEmitter);

KafkaZookeeperMonitor.prototype.connectToZk = function(zookeepers){
    client = zookeeper.createClient(zookeepers);
    client.connect();

    client.once('connected', function () {
        console.log('Connected to ZooKeeper');
        this.emit('connected');
    });
}

module.exports = KafkaZookeeperMonitor;

and I call this from my index.js file as follows:

var KafkaZookeeperMonitor = require('./kafkaZookeeperMonitor'),
    kafkaStatus = new KafkaZookeeperMonitor(),
    brokerPath = '/brokers/ids';

kafkaStatus.connectToZk('192.168.50.252:2181');

kafkaStatus.once('connected', function(){
    console.log('watcher connected to Zookeeper');
})

When I run the code I get the log message

'Connected to Zookeeper'

but the this.emit('connected'); does not seem to fire.

I've looked around on the web and I think I'm setting up my event emitter correctly. Can anybody help me out where I might be going wrong here?

Thanks

for your reference : http://www.sitepoint.com/nodejs-events-and-eventemitter/ — Gopinath Shiva, Jun 25 '15 at 14:29

score 3 · Accepted Answer · answered Jun 25 '15 at 14:34

3

The context of the callback function is not the KafkaZookeeperMonitorz Object so this is not really the Object instance.

This should work:

KafkaZookeeperMonitor.prototype.connectToZk = function(zookeepers){
  var self = this;
  client = zookeeper.createClient(zookeepers);
  client.connect();

  client.once('connected', function () {
      console.log('Connected to ZooKeeper');
      self.emit('connected');
  });
}

The reason it's not throwing an error may be because the client is also extending EventEmitter

answered Jun 25 '15 at 14:34

Maroshii

3,937
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You are correct, thank you for your help – Jon Hunter Jun 25 '15 at 14:40
You helped him too much! Teach all the coders the scope! – Xogle Jun 25 '15 at 14:43
1

@Xogle Yeah... well, it's up to the OP to research and understand why instead of **programming by coincidence** – Maroshii Jun 25 '15 at 14:47
@Maroshii agreed, hopefully OP does because if they continue in the pattern they are going, they will run into many scope issues. :P – Xogle Jun 25 '15 at 14:48

score 1 · Answer 2 · answered Jun 25 '15 at 14:30

1

I don't believe 'this' is what you think it is...

this.emit('connected');

Debug and make sure your 'this' is what you are looking for...

http://javascriptplayground.com/blog/2012/04/javascript-variable-scope-this/

answered Jun 25 '15 at 14:30

Xogle

363
3
16

Node JS event not firing

2 Answers2