Creating Dojo Widgets Programmatically or Declaratively

The Dojo Toolkit has an awesome UI framework called Dijit.  Dijit is an expansive set of Dojo widget that allow you to create highly themeable, functional forms, layouts, and much more.  One of the highlights of Dijit, from a developer's perspective, is that you may create widgets in two ways:  declaratively and programmatically.  This blog posts aims to show you an example of each widget creation method and discuss the advantages of each.

Required: Requiring Classes

Whether you prefer declarative or programmatic widget creation, you always need to require desired widget classes:

dojo.require('dijit.form.FilteringSelect');
dojo.require('dijit.layout.TabContainer');
dojo.require('dijit.layout.ContentPane');

With required class declarations in place, it's showtime!

Option 1: Creating Widgets Declaratively

Creating widgets "declaratively" means to create widgets using HTML markup with attributes to denote that an element should become a widget.  The first part of creating a widget declaratively is to direct dojo to parse the page, looking for Dojo widgets  There are two ways to do this.  The first way is to configure the djConfig variable's parseOnLoad property:

<script src="/js/dojo.js" djConfig="parseOnLoad:true;"></script>

parseOnLoad does exactly what it sounds like: parses the page as soon as all resources and DOM elements are loaded.  The other way is to explicitly tell dojo to parse the page:

//load the parser
dojo.require('dojo.parser');

//parse the page
dojo.ready(function() {
	dojo.parser.parse()
});

Now that Dojo has been told to parse the page once the DOM is ready and Dojo Toolkit assets are loaded, you can create your Dijit widgets using markup.  The dojoType attribute provides a place to declare what type of Dijit widget the element should  become:

<!-- turn a select into a "FilteringSelect" -->
<select dojoType="dijit.form.FilteringSelect">
	<option value="value1">Key 1</option>
	<!-- more options here -->
</select>

<!-- create a layout widget -->
<div dojoType="dijit.layout.TabContainer">
	<div dojoType="dijit.layout.ContentPane"><!-- content 1 here --></div>
	<div dojoType="dijit.layout.ContentPane"><!-- content 2 here --></div>
	<div dojoType="dijit.layout.ContentPane"><!-- content 3 here --></div>
</div>

Boom!  Once the DOM is ready and resources have loaded, the elements with dojoType attributes will be turned into widgets.   Widget options may be added as custom attributes keys and values:

<!-- turn a DIV into a "FilteringSelect"; options will come from data store -->
<div dojoType="dijit.form.FilteringSelect" store="optionsStore" searchAttr="val">
	<!-- options come from a data store -->
</div>

<!-- create a layout widget; contentpane has custom attributes for JS -->
<div dojoType="dijit.layout.TabContainer">
	<div dojoType="dijit.layout.ContentPane" closable="true" href="somepage.php" preload="true">
	<!-- content 1 here -->
	</div>
</div>

Sweet, no?  Think of how much time you can save by embedding widget types and options within the elements themselves.

Option 2: Creating Widgets Programmatically

To create a widget programmatically, you create DOM nodes which act as placeholders for the future widget:

<button id="makeMeAWidget">Click Me</button>

Once the DOM and all dependencies have loaded, you must explicitly add JavaScript to turn the HTML element into a widget.

//when dependencies are loaded...
dojo.ready(function() {
	//...make elements into widgets
	var widget = new dijit.form.Button({},'makeMeAWidget'); //options,elementID
});

Instead of individually assigning widgets to elements, you may also use dojo.behavior to find elements by selector and widgetize them:

dojo.behavior.add({
	'button': {
		found: function(button) {
			new dijit.form.Button({},button); //options,elementID
		}
	}
})

Dojo finds all elements that match the  given selector and widget-izes them.

What's Best?

There are a few things you to keep in mind when deciding which is best for your project

• Programmatic widget creation is faster because the DOM doesn't need to be scoured to find elements that should become widgets.
• Declarative widget creation allows you to code (and thus create widgets) faster.  If your page isn't too big, the speed difference between declarative and programmatic widget creation is very small.

So What's Your Excuse?

You've seen what Dijit can do but you haven't tried it yet.  What's your excuse?