Building Ajax-enabled custom web application on top of SharePoint

Ajax seems to be the in-thing for any web application nowadays. It is easy to implement into to existing ASP.NET application and bring huge improvement in the total user experience of a web application.

However, building an Ajax-enabled custom web application on top of SharePoint requires some tweaking before you get the wow effect of Ajax.

1. If the Ajax-enabled custom application uses the SharePoint master pages, such as default.master master page, remove this SharePoint tag from it: <wssuc:Welcome id="IdWelcome" runat="server" EnableViewState="false"></wssuc:Welcome>. This affects Ajax postbacks. Removing it will partially fix the problem, e.g. one Ajax postback can be made, but subsequently no postbacks.
2. Open LAYOUTS\1033\init.js file and look for javascript function _spFormOnSubmitWrapper. Under “if (_spFormOnSubmitCalled)” code block, remove/comment the “return false;” code. Not sure what is the effect of removing this bit though thus do it on your own risk!

Alternatively, the javascript function _spFormOnSubmitWrapper can be overwritten only on the pages that uses Ajax. This can be done by puting the modified version of the js function to a seperate .js file and reference it right after the line where reference to init.js were made.

Thanx to the post from Vincent Rothwell and comment by Phillip Lanier.