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The primus-emit module adds client->server and server->client event emitting to Primus.


The module is released under the name primus-emit:

npm install --save primus-emit

The --save flags tells npm to automatically add the package and it's installed version as dependency.

Adding it to Primus

The module should be used through Primus's plugin system. In the following examples we assume that your server has been setup as:

'use strict';
var Primus = require('primus')
  , server = require('http').createServer();
  , primus = new Primus(server, { transformer: 'websockets' });

Now that the server and Primus instance has been created we can add the plugin with the server. Adding plugins is done with the primus.use method:

primus.use('emit', require('primus-emit'));

And that is everything that you need. The module doesn't require any configuration.

If you are manually saving the compiled Primus client to disk make sure you include the plugins before calling the, primus.library or primus.Socket methods or properties as you will be compiling the client file without the added plugins.


There are a couple exceptions on the events that you can emit between the server and client. We automatically blacklist reserved event names. This ensures that you cannot accidentally emit the end event on the client and close the connection on the server etc. The blacklisted events are all events that are prefixed with incomming: and outgoing: as they are used by Primus internally and all events client or server emits. See for an overview of all events that are emitted by Primus.


To emit an event from the server to the client you can simply call the emit method:

primus.on('connection', function connection(spark) {
  spark.emit('event-name', 'arguments');
  // To receive events, simply add a listenern for it. 
  spark.on('custom-event', function custom(data, another, arg) {
    assert.equal(, 'foo');
    assert.equal(another, 1);
    assert.equal(arg, 'bar');
    this.emit('foo', 'bar');


If you want to send an event to every connected client on your server you can simply do that by iterating over the connections.

primus.forEach(function (spark) {
  spark.emit('broadcast', 'event');


Sending events on the client is just as simple as on the server.

var primus = new Primus('http://localhost:port');
// We can listen to events that are emitted from the server. 
primus.on('event-name', function (arg) {
  assert.equal(arg, 'arguments');
  // Or emit our own events to the server. 
  this.emit('custom-event', { foo: 'foo' }, 1, 'bar');
primus.on('foo', function (bar) {
  assert.equal(bar, 'bar');
  primus.emit('foo', bar);


How is different than primus-emitter

There are a couple of differences between this module and the primus-emitter module. The only similarity that they have is that they both emit events. The main differences are:

  1. method name The primus-emitter module adds a special send method to the prototypes while we re-use the emit method. This makes the code much more portable as it uses the same method name node's EventEmitter.
  2. Focus This module only focuses on one thing, emitting events. The primus-emitter ships with a lot more features that are not needed for emitting events.
  3. Small The footprint of this module is really small. The whole code base is only 80 lines of code including comments. We use the bare minimal code in order to work. This makes maintenance a lot easier.

Why was this module created

This module was written as part of the plugin documentation for Primus. Writing an EventEmitter was the ideal use case as it:

  • Uses the Primus message transformation for message interception.
  • Extends the client and server.
  • Is small enough to understand.