A brief look at Yahoo! Event Utility [addListener]

I’ve been getting familiar with the Event Utility in the Yahoo library , and it’s a great way to handle and manage javascript events in a clean centralized way. It also smooths out the differences between browser event handling so you no longer need lines like this in your event functions:

e  = e ? window.event;

If you’re unfamiliar with events, it might help to read the article on quirksmode, as well as the yui page.

This library has lots of great methods for event listening, creating custom events, passing objects to event handler functions (a great feature), stopping default event behavior, and attaching listeners to all elements of a particular class rather than cluttering up your code with hundreds of individual listener calls. It’s all encapsulated in neat, well-documented code and a clear API.

One current simple example. I’m building a project where there’s a text input field on stage that serves as a quick “editor”: the user types a number into the field that corresponds with an object on the stage, and then they hit ENTER. [Result: they land in the object in an open editor, saving them mouse-action on the stage and allowing for easy keyboard access to dispersed elements]. We’re not actually submitting a form and since the text area is embedded in another form we just want to listen for the ENTER key but disable form submission, which automatically happens on enter. We also need to make sure that if the user double-clicks within the text area, the usual dblclick behavior (which creates a new object) is disabled. So we want this editor to listen for two events: keydown and dblclick; as well as stop the default behavior of the enter key (submitting the form).

Instead of something like this [pseudo-but-close code]:

< input type="text" id="editor"
onkeydown="javascript:edit();return false"

ondblclick="javascript:return false;" />

We can simply write

< input type="text" id="editor" />

And then in script tags in a centralized location,

$E = YAHOO.util.Event;

$E.addListener('editor', 'keydown', edit);
$E.addListener('editor', 'dblclick', interceptAction);

The first argument is name of the id of the element in question (or an element object itself); the second is the javascript event to listen for; and the third is the name of your function. There’s an optional 4th argument, obj, which is an arbitrary object you can pass to your handler. If you do this, define your handler with two arguments: (e,obj).

Then define your functions:

/* handler to open your editor */

var edit = function(e){
// GRAB enter key
if( e.keyCode == 13){
// PREVENT form from submitting on enter
//[the default behavior of the enter key]
$E.preventDefault(e);
// DO things here
openInlineEditor();
}
}

/* handler to prevent default actions */
var interceptAction= function(e) {

// STOP the event from propagating to other listeners
$E.stopPropagation(e);
}

This is just the tip of the iceberg. I recommend reading up on this and looking at their examples and related articles linked on the page. It’s made my event handling easier and more fun.

This blog entry was posted on Tuesday, February 13th, 2007 at 11:01 am and is filed under Javascript/AJAX, Languages. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.