NodeList Extensions

Dojo includes a range of extensions to the NodeList collection that is used by dojo/query. In this tutorial, we’ll look at what extended functionality is available and how to put it to good use.

  • Difficulty: Beginner
  • Dojo Version: 1.8

Getting Started

In the earlier tutorial on dojo/query, we saw how to get a collection of nodes matching a query or selector, and how to use the methods on dojo/NodeList to work with those nodes. Let's quickly recap. Here's the markup we’ll be using for most of the demos (we're going with a fruity theme for this tutorial):

The dojo/NodeList object is different from the DOM NodeList object. Dojo's NodeList is an actual instance of an array decorated with extra methods. ES5 iteration methods are guaranteed to be available even in a non-ES5 environment, and as you will see in this tutorial there are various modules that can extend dojo/NodeList with additional useful methods.

<button type="button" id="btn">Pick out fresh fruits</button>

<h3>Fresh Fruits</h3>
<ul id="freshList"></ul>

<h3>Fruits</h3>
<ul>
	<li class="fresh">Apples</li>
	<li class="fresh">Persimmons</li>
	<li class="fresh">Grapes</li>
	<li class="fresh">Fresh Figs</li>
	<li class="dried">Dates</li>
	<li class="dried">Raisins</li>
	<li class="dried">Prunes</li>
	<li class="fresh dried">Apricots</li>
	<li class="fresh">Peaches</li>
	<li class="fresh">Bananas</li>
	<li class="fresh">Cherries</li>
</ul>

To demonstrate dojo/query, a click handler is created for the button:

require(["dojo/query", "dojo/domReady!"], function(query){
	query("#btn").on("click", function(){
		var nodes = query("li.fresh");
		nodes.on("click", function(){
			alert("I love fresh " + this.innerHTML);
		});
	});
});

The query("li.fresh") call returns a NodeList, which is a standard JavaScript array decorated with additional methods that let us work more easily with a collection of DOM nodes. Because each query call returns a NodeList, we can make this even simpler by chaining method calls ( instead of typing var nodes over and over again):

require(["dojo/query", "dojo/domReady!"], function(query){
	query("#btn").on("click", function(){
		query("li.fresh").on("click", function(event){
			alert("I love fresh " + event.target.innerHTML);
		});
	});
});
View Demo

Troubleshooting chains of method calls can be difficult, as there is nowhere to add logging statements or breakpoints in the debugger. Break apart the chain into discrete steps to inspect what each method returns.

Doing More with NodeList

This pattern of getting some nodes and doing something with them is pervasive enough that many potential features of NodeList end up conflicting with the modular nature of Dojo and a focus on providing "composable" functionality. As a result, in Dojo and DojoX, there are a variety of NodeList extension modules that can be loaded to add new functionality to NodeList as necessary. Let's take a look at them now.

A Note on Documentation

In the API viewer, the NodeList object is displayed with all the extensions to it that are declared in all the extension modules from both Dojo and DojoX. Although the source module is identified, it is rather "complex". In addition the individual modules which extend the object are essentially "blank". In the reference guide though, each module has its own page (e.g. the dojo/NodeList-data page) which makes it clearer what methods are provided by that module.

Working with Styles and DOM

Prior to Dojo 1.7, the base NodeList featured DOM methods such as addClass, removeClass, attr, style, empty, and place. With the advent of AMD and Dojo 1.7, these methods have been moved to dojo/Nodelist-dom. Here's an example of how you use that module:

require(["dojo/query", "dojo/NodeList-dom"], function(query){
	query("li.fresh")
		.addClass("fresher")
		.attr("title", "freshened")
		.style("background", "lightblue")
		.on("click", function(){
			alert("I love fresh " + this.innerHTML);
		});
});

Simply loading the dojo/NodeList-dom module adds these methods to NodeList. They act exactly as they do with dojo/dom and related modules.

Animating Elements

The dojo/NodeList-fx module augments NodeList with a series of methods that allow you to apply effects from Dojo's effects system to a collection of nodes. These methods function identically to their non-NodeList counterparts, so take a look at the Dojo Effects and Animation tutorials if you aren't familiar with them.

In this demo, we’ll use the same fruity list, and a button that executes the following code when clicked:

require(["dojo/query", "dojo/NodeList-fx", "dojo/domReady!"], function(query){
	query("#btn").on("click", function(){
		query("li.fresh")
			.slideTo({
				left: 200, auto: true
			})
			.animateProperty({
				properties: {
					backgroundColor: { start: "#fff", end: "#ffc" }
				}
			})
			.play();
	});
});
View Demo

Unlike most NodeList methods, NodeList-fx methods return an animation object by default, which conflicts with the normal chaining behavior of NodeList. This is because Dojo’s animation functions normally return an animation object, and it is up to you to call play on that object to start the animation. To cause a NodeList-fx method to automatically play the animation and return a NodeList instead, set auto: true in the object passed to the function, as demonstrated above in the slideTo call.

Associating Data with Elements

The dojo/NodeList-data module adds a mechanism for attaching arbitrary data to elements via the data method. Here is an example that stashes a Date object on an element each time it is clicked:

require(["dojo/query", "dojo/NodeList-data", "dojo/domReady!"], function(query, NodeList){
	function mark(){
		var nodeList = new NodeList(this);		// make a new NodeList from the clicked element
		nodeList.data("updated", new Date());	// update the 'updated' key for this element via the NodeList
	}
	
	query("li")							// get all list items
		.data("updated", new Date())	// set the initial data for each matching element
		.on("click", mark);				// add the event handler

	query("#btn").on("click", function(){
		query("li").data("updated").forEach(function(date){
			console.log(date.getTime());
		});
	});
});
View Demo

Here, we’re doing three things:

  • Associating an initial Date object with each element.
  • Setting up a click handler to call the mark() function
  • Setting up a button that allows us to view the data for each item.

Inside the click handler, we still need a NodeList to get at the data properties for the clicked element, so we create a new one from the element that was clicked. The existing Date object on the clicked element is then replaced with a new one.

With NodeList-data, it is extremely important that you call removeData on the NodeList when removing elements from the DOM. If this is not done, your application will leak memory, since the data is not actually stored on the element itself and will not be garbage collected even if the node itself is.

Moving Around the DOM

The dojo/NodeList-traverse module adds methods to NodeList that allow you to easily move around the DOM to find parents, siblings, and children of reference nodes.

To illustrate, we’ll use a longer, categorized list of fruit. Some fruits have been marked as tasty (with the class of yum), and we want to be able to:

  1. Highlight them.
  2. Indicate in the header for that list that there’s goodness inside.

Using the methods provided by NodeList, dojo/NodeList-traverse and dojo/NodeList-dom, here is one quick way to do that:

require(["dojo/query", "dojo/NodeList-traverse", "dojo/NodeList-dom", 
		"dojo/domReady!"], function(query){
	query("li.yum")				// get LI elements with the class 'yum'
		.addClass("highlight")	// add a 'highlight' class to those LI elements
		.closest(".fruitList")	// find the closest parent elements of those LIs with the class 'fruitList'
		.prev()					// get the previous sibling (headings in this case) of each of those fruitList elements
		.addClass("happy")		// add a 'happy' class to those headings
		.style({backgroundPosition: "left", paddingLeft: "20px"}); // add some style properties to those headings
});
View Demo

The chain here starts with an initial query to find the list nodes we're interested in, then uses traversal methods to move up and sideways to find the heading elements associated with the lists that contain those list nodes.

The important thing to understand with the traversal methods is that each call returns a new NodeList containing the results of your traversal. Methods like closest(), prev(), and next() are essentially sub-queries, with the nodes in the current NodeList being used as a reference point for the next sub-query. Most of these methods function identically to traversal methods in jQuery and should feel very familiar to users of that library.

Manipulating Elements

The dojo/NodeList-manipulate extension module complements the traverse module by adding some methods for manipulating the nodes in a NodeList. This module adds methods mirroring jQuery's manipulation methods.

The following example puts some of these capabilities to use. Using the same categorized list of fruits, it builds two new lists of yummy and yucky fruits:

require(["dojo/query", "dojo/NodeList-manipulate", "dojo/domReady!"],
function(query){
	query(".yum") // get elements with the class 'yum'
		.clone() // create a new NodeList containing cloned copies of each element
		.prepend('') // inject a span inside each of the cloned elements
		.appendTo("#likes"); // insert the clones into the element with id 'likes'

	query(".yuck")
		.clone()
		.append('')
		.appendTo("#dontLikes");
});
View Demo

The key to this demo is the use of the clone method to create duplicates of the original elements. As with the NodeList-traverse methods, clone returns a new NodeList containing all newly cloned elements which are then modified and appended to the DOM. If clones were not created, the original elements would have been modified and moved instead.

Advanced Content Injection

The dojo/NodeList-html module brings the advanced capabilities of dojo/html::set() to NodeList. Here's a simple example of its use, in which we turn a simple list into a checkbox list using dijit/form/CheckBox widgets:

require(["dojo/query", "dojo/_base/lang", "dijit/form/CheckBox", "dojo/NodeList-html", "dojo/domReady!"], 
function(query, lang){
	var demo = {
		addCheckboxes: function(q) {
			query(q).html('<input name="fruit" value="" data-dojo-type="dijit/form/CheckBox">', {
				onBegin: function(){
					var label = lang.trim(this.node.innerHTML), 
						cont = this.content + label;
					cont = cont.replace('value=""', 'value="'+lang.trim(this.node.innerHTML) + '"');

					this.content = cont;
					return this.inherited("onBegin", arguments);
				},
				parseContent: true
			});
		}
	}

	query("#btn").on("click", lang.hitch(demo, "addCheckboxes", "li.alkaline"));
});
View Demo

With the rich capabilities offered by other NodeList methods, especially those in NodeList-manipulate, the NodeList-html module is probably not one you will use very often, if at all. It is mentioned here nonetheless because it can still be useful as a specialized tool to solve a certain class of problems that would be much more difficult to solve in other ways.

Conclusion

NodeList modules extend the existing NodeList API without bloating your code with features you won't use. By using some of these extensions in your code, you will be able to work with the DOM much more effectively and efficiently.

Error in the tutorial? Can’t find what you are looking for? Let us know!