javascript - Retrieve if an Updatepanel has made a postback -

can tell me if can retrieve javascript above asp.net updatepanel had made asynchronous postback ?

thank's !

have tried registering startup script in updatepanel? this:

scriptmanager.registerstartupscript(this.updatepanelid, typeof(string), "updatepanelscript", "alert('from updatepanel');", true); 

here's link documentation: http://msdn.microsoft.com/en-us/library/bb359558.aspx