YUI 3 Preview Release 2 - IO

Today I will go over the new IO Utility in the YUI 3 Preview Release 2

"IO is an HTTP utility that enables HTTP requests while maintaining a persistent client UI, for the purpose of data retrieval and content update. IO uses the XMLHttpRequest object for making "same-domain" requests. IO can make "cross-domain" requests, when instructed to do so, using an alternate HTTP transport."


What does this mean really? This means we have a single, consistent, interface to various data sources we may point our UI at. This data may be from our site, or another data provider on a different site. When the data resides on our site IO will use XHR (XMLHttpRequest ) to request the data, standard "AJax". When we are making our request cross-domain, the IO utility will use a flash swf to make the call, along with a crossdomain.xml (to let the flash know which sites it has access to). The crossdomain.xml is fairly important on a https: site as IE will complain to no end that you are trying to access non secure data, or mixing secure with non-secure.  The crossdomain.xml resides in your document root.

So, let's see what the YUI 3 team has given us. The basic example provided at the IO Utility page sets up the use of io-base, defines a completed function, and subscribes to the event. The key here seems to be subscribing to the event :

// Subscribe to event "io:complete", and pass an array
// as an argument to the event handler "complete". Since
// "complete" is global.
// At this point in the transaction lifecycle, success or
// failure is not yet know.
Y.on('io:complete', complete, this, ['lorem', 'ipsum']);

When the Y.io(uri) event "complete" finishes, we want to run "complete" function with "this" as the context of execution, and pass also an array ['lorem', 'ipsum']

This may be quite different and confusing to just about every other Framework out there. But so much better! There are a few posts on nabble where people are asking why the IO isn't "seperate" for each request, and the answer lies above. IO is a presistant connection, and it has a context that it runs in. If you are specifying IO in the global context, then all your requests are going to be in the global context, which is specified by "this".

In other words, Event handlers run in thier own context, so you could have multiple listeners on the io:complete event, but only some would run depending on context:    Therefore, you could register a GlobalEvents object and set that context, just as in the examples and this would run for every IO request. If however, you have objects with different scopes, the global would fire as well as the callbacks in different scopes that are set to listen for io:complete.  

The new IO utility also offers a "queue" which you can start, stop, promote, purge, and set the size. This is a big step in ajax frameworks as most like prototype do not come with these capabilities built in. With a queue you can send transactions and gracefully monitor and manage them with the io events and queue commands.

One way I can see this being very useful is if you had created a queue on page onload to load various items not immediatly visible to the user. But say the user then clicks on one of the items, we can immediatly stop the queue, and promote that request to the top of the queue, and when that completes, continue with the loading of the rest of the items! This is, to say the lease, very useful.

YUI 3 Preview Release 2 - Get Utility

Yahoo's User Interface Get Utility is one of my favorites. I use this constantly to load secondary scripts on the page, or when some event requires additional scripts. For example, while putting together a RIA with dialogs, you may not need the "container" library to load when the page loads, you may want to delay this till the user actually performs and action the requires the container to show.

// Code in main page
 

(function(){
    var $Y = YUI();
    ele.on('click', function(){
        $getScripts = $Y.Get.script('/js/myDialog.js', {
            onSuccess: function(){
             // I ran myDialog.js .. assume here that it render()s the dialog
             dialog.show();
             // Do other things
        }});
    }

})();

This is much unchanged from YUI 2.6, and if your upgrading from 2.6 you would find this an easy "fix" to port to YUI 3. Most likely you will also have your own alias variable and namespace you can integrate this into.

In the above code we are using $Y.Get.script to get a single script and load it. Usually with these files I will use the (function(){ ... })(); convention. This makes it a little more clear what the code will do. If I have created namespaces, I will give each file it's own namespace and use it throughout the file.

This does a couple things. If used on page load, the scripts will be retrieved in a non-blocking manner. In other words, your images and CSS will not be in contention with the loading of these scripts. You will also be able to delay the loading of some scripts until they are actually needed.

Some practical applications you could use this for possibly is loading the validation logic on form submit, loading dialogs, calendars, and any of the heavier widgets that are not visible on first load. 

Up Next :  IO

YUI Shed Presents - YUI 3.x Preview Release 2

    YUI 3.x has been brewing for some time now under the radar. I personally have kept peeking in to see if they had any of the widgets from YUI 2 working in this latest releases. As of YUI 3.x Preview Release 2 We have the first widgets, Overlay, Slider, and Console, along with MenuNav Nodes. This is a pretty big step forward, and gives me incentive to give each new component a test run, and provide a bit of practical use code. Over the next few days I will dive into each of the new components and give some use case code.

"Stay Tuned!"

Nicole Sullivan on YUI Theater

This was a very good installment of YUI theater, that all web developers should take a look at. Her talk goes into image sprites, things already recommended by YSlow!, and some very interesting points to consider when designing a website. Sometimes, a few bad requirements will make things difficult to maintain, as well as make for bad markup and or bad javascript.

If you have never visited YUI Theater, your in for a treat. I highly recommend *ALL* of the videos there. Crockford is "the man".

YUI and Google Gears Data Sets

I recently have had some requests to post some examples of how to use YUI with Google Gears. Below is the code for a simple example using the developer's example from Google Gears documentation as a starting guide.

       
var loader = new YAHOO.util.YUILoader({
                
  require: ['json', 'datatable'],
  onSuccess: function(){
    var db = google.gears.factory.create('beta.database');
    db.open('database-test');
    db.execute('create table if not exists Test' +
               ' (Phrase text, Timestamp int)');
    db.execute('insert into Test values (?, ?)', ['Monkey!', new Date().getTime()]);
    var rs = db.execute('select * from Test order by Timestamp desc');
                        
    // Create an object to hold the Results
    ResultSet = {rows: []};
      
    var fieldCount = rs.fieldCount();
    count = 0;
    
    while (rs.isValidRow()) {
      count++;
      var tmp = {};
      for (x = 0; x < fieldCount; x++) {
        // Add Each field to tmp object    
        tmp[rs.fieldName(x)] = rs.field(x);
       }
       // Push object onto Results
       ResultSet.rows.push(tmp);
       rs.next();
    }
    rs.close();
                        
    // YUI DataSource
    var dsLocalJSON = new YAHOO.util.LocalDataSource(ResultSet);
    dsLocalJSON.responseType = YAHOO.util.XHRDataSource.TYPE_JSON;
    /* Could also use rs.FieldName here to do dynamic */
    dsLocalJSON.responseSchema = {
      resultsList: "rows",
      fields: ["Phrase", "Timestamp"],
      meta: {
        totalRecords: count
      }
    };
                        
    /* Colum Definitions */
    var ColDefs = [{
      key: 'Phrase',
      label: "The Phrase"
    }, {
      key: 'Timestamp',
      label: 'Epoch',
      sortable: true
    }];
                        
    var DataTable = new YAHOO.widget.DataTable('datatable', ColDefs, dsLocalJSON);
  }
}).insert();
                
       

You will of course have to add the proper CSS and JS include files. For this example I used the datatable.css in the sam skin directory, the gears_init.js and YUI Loader js file. You will also need a div with and id='datatable'.

This example will use the loader to get the datatable javascript, as well as the json library. You can use the json library to parse out the record rows you don't need with this.

Hope this helps some people!