Improving Node.js: Faye

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As we mentioned in a previous post, node.js is a very powerful tool that allows us to create servers using JavaScript as the server-side programming language, but it can be costly to create certain tools and protocols from scratch. Faye is a layer (extension) on top of node.js, logically written in JavaScript, that creates a publish-subscribe system for message channels based on the Bayeux protocol.

In other words, faye is responsible for managing channels, message delivery, and reception by subscribers to those channels. Faye consists of two parts: one on the server side and another on the client side (also written in JavaScript). To explain how faye works more easily, let’s look at an example: Imagine we are creating an application that needs to send real-time notifications to all users connected to a page. In our node.js script, we introduce the following:

var Faye = require('faye'),
  server = new Faye.NodeAdapter({ mount: '/' });
server.listen(8000);

and we launch node.js

$ node faye.js

Now on the client, we load a JavaScript file with this content:

var client = new Faye.Client('<a href="http://localhost:8000/">http://localhost:8000/</a>');
client.subscribe('/messages', function (message) {
  alert('Got a message: ' + message.text);
});

With these two simple operations, all users connected to our website will be subscribed to the messages channel and will be ready to receive information. To send a message from one of the clients, which could be our website’s control panel, we execute the following JavaScript:

client.publish('/messages', { text: 'Hello world' });

And immediately, an alert with the message “Hello world” will appear in all the visitors’ browsers. This is an example taken from the Faye website, but I wanted to explain it with a practical example. As you can see, the potential and simplicity of this system is great, since we can send more variables than just message if needed (for example, number of unread messages, date, etc.); we can also have several different channels to send different types of information or only subscribe certain users to those channels. In a future post, I will explain how to manipulate messages on the server side—for example, to store them in a database, send messages from the server itself, etc.

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