Using Jquery Onbeforeunload Event In Application?

I am using jquery onbeforeunload event in asp.net application.
If i write event as given below then its working fine and display confirm dialog box.

var vGlobal = true;
var sMessage = "Leaving the page will lost in unsaved data!";
[ Working ]
> window.onbeforeunload = function() {
> if (vGlobal == false) return
> sMessage; }

but its not working if i use bind method like as given below

[ Not working ]
$(window).bind("beforeunload", function(e) {
if (vGlobal == false)
return sMessage;
});

Is there any difference between these two methods.

Code on aspx:

<asp:TextBox ID="txtName" runat="server"></asp:TextBox>
CLICK ON THIS LINK TO SEE RUNNING EXAMPLE