Using Pub Sub with The Dojo Toolkit

By  on  

As I've stated many times, the Dojo Toolkit is probably the most complete JavaScript toolkit out there, especially when it comes to event management and application communication.  I've already done a very brief introduction to dojo.connect so I thought I'd also do a short introduction to Dojo's other event system:  pub/sub with dojo.publish and dojo.subscribe.

The publish/subscribe strategy has many advantage over basic event connectivity:

  • No reference to another object or element is required
  • It's not the concern of the publisher who subscribes
  • As a result of not needing reference to another object or element, your code is instantly more portable

So let's take a look at how pub/sub is used!


The first part of pub/sub is publishing to a channel.  When publishing to a channel, you provide the channel name and arguments to be passed to any subscriber:

// dojo.publish("{channel}", [arg1, arg2, arg3]);
dojo.publish("/app/login", [username, userData]);

Arguments should be passed within an array and may be of any type.  Your channel can be any number of channels deep; the more specific the channel, the more specific your event can be.  While the slash is used as the standard channel specifier, you can use any string name you'd like.


dojo.publish broadcasts message but it's dojo.subscribe that that must listen for and react to the message.  You must match the exact channel name when subscribing:

// Subscribe to the same channel, accepting each argument individually
var handle = dojo.subscribe("/app/login", function(username, userData) {
	// Now do something!
	// Unsubscribe if you want

Note how a handle is returned from dojo.subscribe. The Dojo Toolkit does not support wildcard channel subscription, so the following will not work:

// Wildcards don't work!
var handle = dojo.subscribe("/app/*", fn);

So how is pub/sub used internally within Dojo?  One prime example is the dojo.hash method.  dojo.hash notifies you of when the window hash changes.  You can catch the hash change event by subscribing as follows:

// This is how you respond to hash changes!
dojo.subscribe("/dojo/hashchange", function(currentHash){ 
	// Do something!

Now you can modify AJAX-ified portions of your application when the hash changes!

What's great about pub/sub in any toolkit or platform is that it's easy to both use and code the API for.  The code and idea are both very simply yet also very powerful.  If you've got a large application that you'd like to be flexible and decoupled from individual objects, try using pub/sub -- it will relieve unnecessary complexity!

Track.js Error Reporting

Upcoming Events

Recent Features

  • Send Text Messages with PHP

    Kids these days, I tell ya.  All they care about is the technology.  The video games.  The bottled water.  Oh, and the texting, always the texting.  Back in my day, all we had was...OK, I had all of these things too.  But I still don't get...

  • Write Simple, Elegant and Maintainable Media Queries with Sass

    I spent a few months experimenting with different approaches for writing simple, elegant and maintainable media queries with Sass. Each solution had something that I really liked, but I couldn't find one that covered everything I needed to do, so I ventured into creating my...

Incredible Demos

  • Introducing MooTools Dotter

    It's best practice to provide an indicator of some sort when performing an AJAX request or processing that takes place in the background. Since the dawn of AJAX, we've been using colorful spinners and imagery as indicators. While I enjoy those images, I am...

  • Create a Spinning, Zooming Effect with CSS3

    In case you weren't aware, CSS animations are awesome.  They're smooth, less taxing than JavaScript, and are the future of node animation within browsers.  Dojo's mobile solution,, uses CSS animations instead of JavaScript to lighten the application's JavaScript footprint.  One of my favorite effects...


    Wrap your code in <pre class="{language}"></pre> tags, link to a GitHub gist, JSFiddle fiddle, or CodePen pen to embed!