node.js events in router(emitter) and handlers(listeners)

Question

My need is to generate custom events in router, that shall be based on the data that is coming from front-end. Like if the front-end object has handle_hello_world, then the router shall emit an event for handle_hello_world, so that the corresponding event listener can wake up and handle the request. The callback from this listener should again go back to router and then back to the front-end.

I tried my hands with normal events emitters in node.js that would emit and receive events within the same scoped file. But I failed to do the desired linkage from router -> handler -> router again.

Any help with events, streams, bacon, event bus, publisher-subscriber, socket.io, etc. would be handy as my knowledge in node events is not great.

monkey · Answer 1 · 2015-07-19T14:13:44.940

0

With Express and node EventEmmiter You can do something like:

var emitter = require('events').EventEmitter;

emitter.on('myEvent', function(cb) {
  //do something

  var data = 'some data';

  cb(data);
});

emitter.on('myEvent', function(cb) {
  //do something

  var data = 'other data';

  cb(data);
});

app.use('/path', function(req, res, next) {
  var eventName = 'myEvent';
  var listenersCount = EventEmitter.listenerCount(emitter, eventName);

  emitter.emit(eventName, function(dataFromEventHandler) {
    listenersCount--;
    if (!listenersCount) {
      //all listeners completed
      //do something else...
      next();
    }
  })
});

eventName you can get from req.body or req.params. This is Express docs http://expressjs.com/4x/api.html#req.params

edited Jul 19 '15 at 14:13

answered Jul 19 '15 at 12:37

monkey

1,279
14
15

Not finding it straight forward to split emitter and listener. – user3601166 Jul 19 '15 at 12:52
If you do not like callbacks may want to look at generators and async functions http://koajs.com – monkey Jul 19 '15 at 13:05
Not really issue with callbacks or events within one file, but I think more information is needed on how events emitted from router can be picked by 1-n listeners that are registered to router events. – user3601166 Jul 19 '15 at 13:30
fixed: added listenersCount – monkey Jul 19 '15 at 14:14
you can write a simple wrapper for that – monkey Jul 19 '15 at 14:18

node.js events in router(emitter) and handlers(listeners)

1 Answers1