Sys.Application.add_load(ApplicationLoadHandler)

function ApplicationLoadHandler(sender, args)
{
     Sys.WebForms.PageRequestManager.getInstance().add_endRequest(pageLoaded);
     
}

function pageLoaded(sender, args)
{
    document.forms[0].action = requestUrl;
    document.forms[0]._initialAction = requestUrl;
}

if (typeof(Sys) !== 'undefined') Sys.Application.notifyScriptLoaded();