ASP.NET: How does ASP.NET Ajax work?

SYS namespace

• SYS namespace represents the root namespace for the Microsoft Ajax Library. Sys is not a server side namespace. ASP.NET Ajax registers its clientside library when you use scriptmanagers and updatepanels. That’s the javascript that’s used to handle the Ajax calls from the updatepanel behind the scenes. These Ajax requests are handled through the PageRequestHandler. A lot of ASP.NET Ajax namespaces and classes are in fact accessible to javascript. They typically reside in Sys.* namespaces.
• Usage
  [js]
  
  [/js]

add_pageLoaded

• The pageLoaded event is raised after all content on the page is refreshed, whether it was refreshed because of a synchronous (full-page) postback or an asynchronous postback. You can use this event to provide a custom transition effect for updated content.
  [js]
  
  
  [/js]