Sido van Gennip

Building a Flashcard Widget with jQuery UI

Last couple of weeks I’ve been playing around with jQuery UI. As a framework it’s a pretty nice way to add a bit of structure to your code. At the heart of this framework is The Widget Factory, which is a sort of template for building your component (visual or not).

To give quick run through of how to build stuff using widgets, I’m going to build a Flashcard Widget. A flashcard is a simple learning aid to test your memory. One side of the card presents a question and the other has the answer to that question. This is what we are going to build:

Just click on the card to see the answer. I’ve used a definition list for html as shown below. Gave the the container (<dl>) a width and a height and made <dt> and <dd> 100% for both width and height and absolute positioned them on top of each other.

HTML
 <dl id="myFlashcard">
   <dt>Who ya gonna call?</dt>
   <dd>GHOSTBUSTERS!</dd>
 </dl>

CSS
/* a bit simplyfied */
 .ui-flashcard {
   height: 150px;
   position: relative;
   width: 350px;
 }
 .ui-flashcard dt,
 .ui-flashcard dd {
   height: 100%;
   left: 0;
   position: absolute;
   top: 0;
   width: 100%;
 }
 .ui-flashcard dd {
   z-index: -1;
 }

Now let’s add some behavior to our widget! If you ever create class definition in a programming language (like PHP for example) a widget is a lot like that. To define a widget type you use the .widget method like: $.widget("ui.flashcard", { /* definition */ }). You’ve got a method _create which is called on creation and _destroy is called on destruction to cleanup. Just like the constructor and deconstructor.

Applying a widget (like creating an instance) is the same as using a plugin: $("#myFlashcard").flashcard({ /* options */ }).

Now lets add some classes to our html (using the widget) which can later be used to make it pretty for example:

JS
 $.widget("ui.flashcard", {
   _create: function() {
     this.element
       .addClass("ui-flashcard ui-widget")
       .find("dt, dd")
         .addClass("ui-widget-content ui-corner-all")
     ;
   },
   _destroy: function() {
     this.element
       .removeClass("ui-flashcard ui-widget ui-corner-all")
       .find("dt, dd")
         .addClass("ui-widget-content")
     ;
   }
 });

Now for letting it actually do something we create a method called show, as in “show me the answer please”. Here we simple fade out the <dt> so the answer (<dd>) becomes visible.

JS
 show: function() {
   this.element.find("dt").fadeOut("slow");
 },

This can now be called with: $("#myFlashcard").flashcard("show"). We can also bind this to a custom event called “show” like:

JS _create: function() { var widget = this; this.element .bind(“show”, function() { widget.show(); })  ; },

Now to finish things we bind the “click” event on <dt> to our “show” event and we got a working flashcard widget!

JS
 _create: function() {
   var widget = this;
   this.element
     .find("dt")
       .click(function() {
         widget.element.trigger("show");
     })
   ;
 },

Here is the final widget code and I also created a gist of the full example. And the story continues at: It’s nice to have some options, in your custom UI Widget that is!