Sys.WebForms.PageRequestManager dispose Method
Releases ECMAScript (JavaScript) resources and detaches events.
Sys.WebForms.PageRequestManager.get_Instance().dispose();
Remarks
Use the dispose method to free client resources. The PageRequestManager instance calls the dispose method during the window.unload event of the browser. If you call the dispose method and then reference members of the PageRequestManager class, an error occurs. In typical page developer scenarios, you do not have to call the dispose method.