Nowadays using Ajax for a web application becomes a default choice. The real challenge is choosing the right Javascript library for the application.
Today we have plenty of Javascript frameworks which are greately reducing the development time for front-end development.

Here I am coming up with the comparision criteria for evaluating the frameworks.

1. DOM navigation/manipulation
2. Basic UI components support
3. Advanced UI widget library
4. Themes and skinning support
5. Validations support
6. Ease of server interaction
7. Multiple data exchange formats support

1. DOM navigation/manipulation:
    DOM navigation/manipulation is the core feature needed while building an ajax based rich application.
    
2. Basic UI components support:
    Any Javascript framework user expects the following UI components support that are necessary to develop even a simple ajaxified web app.
    Form Controls such as TextBox, Radio buttons, Checkboxes, Dropdowns, Calendars, Date Time pickers, Color Picker etc.
    
3. Advanced UI widget library:
    Now a days any Ajaxified web application needs the following advanced UI widget to develop RichUI.
        a) Grid/DataTable with pagination, sorting and filtering.
        b) AutoComplete
        c) Tab/Tree View
        d) Layout managers
        e) Popup dialogues
        
4. Themes and skinning support:
    Javascript tool kit should support theme or skin changes with minimal changes.
    
5. Validations support:
    The web application which is presenting the dynamic content and taking the user input will definitely need several kinds of validation support.
    Required, Email, Numeric, Regex validations are bare minimum validations needed.

6. Ease of server interaction:
    Server interaction is a must feature for an ajax library. The ajax library should provide easy to use ways of getting the data from server and posting the content onto the server. Also it should support binding the result got from server to UI widgets.
    
7. Multiple data exchange formats support:
    XML is the default data exchange format for Ajax. But recently JSON is being preferred than XML. So at a minimum it should support both XML and JSON.

 Guys,

Please share me your thoughts on this.