.NET - ASP.NET AJAX

The following are the limitations of AJAX:

• It is difficult to bookmark a particular state of the application.
• Function provided in the code-behind file do not work because the dynamic pages cannot register themselves on browsers history engine automatically.
• If JavaScript is disabled, then AJAX is not able to perform any work.
• Response time may be slow because different controls of a page are loaded at different time.

The differences between AJAX and JavaScript are given as follows:

• AJAX sends request to the server and does not wait for the response. It performs other operations on the page during that time. JavaScript make a request to the server and waits for response.
• AJAX does not require the page to refresh for downloading the whole page while JavaScript manages and controls a Web page after being downloaded.
• AJAX minimizes the overload on the server since the script needs to request once while JavaScript posts a request that updates the script every time.

The UpdatePanel control specifies the portions of a Web page that can be updated together. As the UpdatePanel control refreshes only a selected part of the Web page instead of refreshing the entire page with a postback, you get more flexibility to create rich and client-centric Web applications.

Refreshing a selected part of the Web page is referred as partial-page update. You can add one or more UpdatePanel control in the Web page, which automatically participates in partial-page update without custom client script. The UpdatePanel control uses the UpdatePanel class to support the partial-page rendering.

The DynamicPopulateExtender control populates the contents of a control dynamically. It enables you to send an asynchronous call to the server that dynamically populates the contents of a control. The DynamicPopulateExtender control replaces the contents of a control with the result of a Web service or page method call.