O'Reilly

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!

Publishing

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.

Subscribing

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
	dojo.unsubscribe(handle);
});

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

Recent Features

Incredible Demos

  • CSS Tooltips

    We all know that you can make shapes with CSS and a single HTML element, as I've covered in my CSS Triangles and CSS Circles posts.  Triangles and circles are fairly simply though, so as CSS advances, we need to stretch the boundaries...

  • AJAX Page Loads Using MooTools Fx.Explode

    Note: All credit for Fx.Explode goes to Jan Kassens. One of the awesome pieces of code in MooTools Core Developer Jan Kassens' sandbox is his Fx.Explode functionality. When you click on any of the designated Fx.Explode elements, the elements "explode" off of the...

Discussion

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

    Recently on David Walsh Blog

    • Convert Video to mp3

      Let's all be honest for a moment:  we've all ... not paid for ... music.  Whether it was via a file sharing app like Kazaa or Napster, or it was downloading and seeding on bittorrent, or maybe even downloading a music video and ripping its audio,...

    • Sort git Branches by Date

      I'll be first person to admit I don't do as much git repository maintenance as I should.  I rarely delete branches which have been merged, so a git branch execution shows me a mile-long list of branches that likely aren't relevant.  The best way to find branches I've recently...

    • Best Tools and Resources for Web Professionals in 2015

      Looking for the right resources to help you satisfy the needs of your clients? On the lookout for the best tools to help you increase your revenue? Searching for the right software to help you improve your business? Well, then you’ve come to the right place....

    • JavaScript Polling

      Polling with JavaScript is one of those ugly but important functions within advanced front-end user experience and testing practices.  Sometimes there isn't the event you can hook into to signify that a given task is complete, so you need to get your hands dirty and simply poll for...

    • OSCON Portland:  Conference Giveaway and Discount!

      O'Reilly puts on the best web industry conferences in the world.  These conferences include Fluent Conference, Velocity Conference, and the upcoming OSCON in Portland, Oregon from July 20-24.  Open Source Convention (OSCON) is a conference that focuses specifically on open source developers and the tools and possibilities...