Google releases Closure!

When Gmail was released I was very enthusiastic in knowing how they built the application around the Ajax technology. Since Gmail, Google have released many successful web application to the public and now they have decided to release the core javascript library that they used to build these application.

Introducing the Closure library and javascript tools built by Google to build applications that scale! They are open sourcing these tools to the web development community. The toolkit consists of :

Closure Complier - A javascript compiler that is used to optimize the code. The compiler is said to remove dead code and minimize the code. It also checks the syntax, variable references and warn about javascript pitfalls.

Closure Library - Is a broad, modular and cross browser javascript library. Developers can make use of the wide range of UI widgets and controls, server communication, effects, data structures etc etc..

And finally, the Closure Templates - are web templates that are precomplied to efficient javascript. Interesting part of templates is that they are implemented for both javascript and java! Meaning you can use the same template on client and sever side.

But, I really wonder why they named the library "Closure" as it very related to programming language terminologies. I also wonder why they released it into Google Labs if they have been using it. According to Google the Closure started out as 20% projects and all google applications currently use it. Open sourcing such a tool is a great boon to web developers!

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Dynamic loading of ComboBox using ExtJS

Ext JS provide us with a very flexible ComboBox widget that can be loaded locally or remotely (dynamic loading). You can also load the combo box from the server in response to an event like changing selection of another combo box. In this article I am going to walk you through an example of dynamically loading a ComboBox in a form.

For example, we have simple form to add details of country. The fields are country name, population and population type. I will keep the first two fields as normal text fields and population type as a combo box. Upon loading of the form, we need to retrieve the population type and load it into the ComboBox.

The first step would be to create a data store (Ext.data.Store) to hold our dynamically loaded data. Lets assume I have a server side method at URL /testapp/poptype.json that fetches the data from some data repository. So, here is our data store:

var ds = new Ext.data.Store({
      proxy: new Ext.data.HttpProxy({url: '/testapp/poptype.json',method:'GET'}),
      reader: new Ext.data.JsonReader({
      root: 'rows',
      fields: [ {name: 'myId'},{name: 'displayText'}] 
      })
  });

Please note that to load the data into the data store, I will have to call the load method. Next, we need to bind this data store to our form. The binding is done through the store attribute when we configure the drop down in the form. Here is our form:

var addCountryForm = new  Ext.form.FormPanel({
      id:"addCountryForm",
      title:"Add Country Form",
      height:300,
      closable:true,
      style: {margin:5},
      frame:false,
      items:  [{xtype:'textfield',name:'cname',fieldLabel:'Country Name' },
             {xtype:'numberfield',name:'pop',fieldLabel: 'Population'},
             new Ext.form.ComboBox({                        
                        fieldLabel: 'Population Type',
                        hiddenName:'popType',
                        store: ds,
                        valueField:'myId',
                        displayField:'displayText',
                        triggerAction: 'all',
                        emptyText:'Select',
                        selectOnFocus:true,
                        editable: false                        
                    })

            ],
        buttons: [{
            text: 'Save'
        },{
            text: 'Cancel'
        }]
  });

Now, lets have a look at a sample JSON output:

{
 "rows":[
     {"myId": "PT1" , "displayText": "Small"},
     {"myId": "PT2" , "displayText": "Medium"},
     {"myId": "PT3" , "displayText": "Large"}
 ]
}

Hope this article helped you out. Happy coding!

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Change ComboBox's default option using jQuery

I have started heavy use of jQuery in my current project.Today's task was very interesting. I am currently building a data filtering component for my application where form and data display table are loaded dynamically.In this article, I will explain how I did it!

I have a complex form with lots of elements.. In a way, all elements!! User select values from drop down (ComboBox) that are dynamically loaded using Ajax. Upon selecting a value, the next drop down or form element values change or are set. I require to set default values to these dropdowns. Lets take a simple drop down:

<select id="centerTypeDropDown" name="centerType">
    <option value="ASC" selected="selected">ASC</option>
    <option value="NSC">NSC</option>
    <option value="USC">USC</option>
    <option value="IKT">IKT</option>
    <option value="UCC">UCC</option>
</select>

The default selected value is ASC. In my application, these values are loaded using Ajax and the default values may change when user select other form elements or drop down. So, in short, new elements get added into this drop down and the selected value changes. For our example, let's say we need to set the default selection to USC instead of ASC.

Using jQuery I can change the default selection to the required option. Here is how to do it:

$("select#centerTypeDropDown option[selected]").removeAttr("selected");
$("select#centerTypeDropDown option[value='USC']").attr("selected", "selected");

That's it! For jQuery beginners, selector string is the magic string. selector returns a object or collection of objects. Using selectors, I can select any DOM object and then use appropriate methods to manipulate its properties. In this case, I need to change the selected attribute to another option. The first line for code is used to select the current selected value in the drop down and then by using the removeAttr method, I remove the attribute from the option tag. The second line of code is used to set the new selected value. I select the same object again then use attr method to set the appropriate attribute.

The above code works fine when we know exactly what our new default value is. What if we get the values and default value from the server dynamically? For example my JSON returned from the server contains new or additional options and default value. Note that, in above code we specify which option to be selected in the sector string through option[value='USC']. In our case, we cannot hard code the selector string, instead we create it dynamically.

var selectorSrting = "select#centerTypeDropDown option[value='"+ defaultValueObtainedFromServer + "']";
$(selectorSrting).attr("selected","selected");

And that's our final code! Let me know if there are better solutions to this problem. And intersted readers, watch out for the next article on dynamically loading ComboBox using jQuery.

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