How to call webservice on close browser?

<script type="text/javascript">

window.onbeforeunload = function () {



myUnloadEvent();
alert('Calling some alert messages here');

return;



};
function myUnloadEvent() {

var pageUrl = '<%=ResolveUrl("~/Service/Customer.asmx")%>'

var parameters = "{}";



$.ajax({
type: "POST",

url: pageUrl + "/CustomerLogout",



data: parameters,
contentType: "application/json; charset=utf-8",

dataType: "json",



success: OnSuccessCall,

error: OnErrorCall

});

}
function OnSuccessCall(response) {

alert('S');



}
function OnErrorCall(response) {

alert('E');





}




</script>



 Above code may not be working on all browser..
So Second method will work on all browser.
---------------------second  method for all browser--------------------

step 1:
make a webservice(Customer.asmx) which have the function name (CustomerLogout());
--------------------------

step:2
call the service by scriptmanager...
<asp:ScriptManager ID="ScriptManager" runat="server" >

<Services>

<asp:ServiceReference Path="~/service/Customer.asmx" />

</Services>

</asp:ScriptManager>

step:3
make the js file CloseBrowser.js


/** start Js Code

* This javascript file checks for the brower/browser tab action.

* It is based on the file menstioned by Daniel Melo.

* Reference: http://stackoverflow.com/questions/1921941/close-kill-the-session-when-the-browser-or-tab-is-closed

*/
 var validNavigation = false;

function endSession() {

// Browser or broswer tab is closed

// Do sth here ...



Customer.CustomerLogout();



}
 function wireUpEvents() {

/*



* For a list of events that triggers onbeforeunload on IE

* check http://msdn.microsoft.com/en-us/library/ms536907(VS.85).aspx

*/
  window.onbeforeunload = function () {

if (!validNavigation) {

endSession();

}

}

// Attach the event keypress to exclude the F5 refresh

$('document').bind('keypress', function (e) {

if (e.keyCode == 116) {

validNavigation = true;

}

});

// Attach the event click for all links in the page

$("a").bind("click", function () {

validNavigation = true;

});

// Attach the event submit for all forms in the page

$("form").bind("submit", function () {

validNavigation = true;

});

// Attach the event click for all inputs in the page

$("input[type=submit]").bind("click", function () {

validNavigation = true;

});



}
 // Wire up the events as soon as the DOM tree is ready

$(document).ready(function () {

wireUpEvents();



});
   // end js code



------------------
Step 4:
call on pages

<script src="CloseBrowser.js" type="text/javascript"></script>

and also call
<script src="jquery.min-1.4.4.js" type="text/javascript"></script>
or any jquery  Version