var needToConfirm = false;

function setDirtyFlag()
{
needToConfirm = true; //Call this function if some changes is made to the web page and requires an alert
// Of-course you could call this is Keypress event of a text box or so...
}

function releaseDirtyFlag()
{
needToConfirm = false; //Call this function if dosent requires an alert.
//this could be called when save button is clicked
}


window.onbeforeunload = confirmExit;
function confirmExit()
{
if (needToConfirm)
return "You have attempted to leave this page. If you have made any changes to the fields without clicking the Save button, your changes will be lost. Are you sure you want to exit this page?";
}