FIRST AND THE STRONGEST OPTION AJAX.NET
OTHERWISE USING SIMPLE JAVASCRIPT TRY,
"XMLHTTPREQUEST"
function postdatain_background(var1,var2)
{
oHttp = window.ActiveXObject ? new ActiveXObject("Microsoft.XMLHTTP") : new XMLHttpRequest();
oHttp.open("GET","www.yourpage.com?arg1="+var1+"& arg2="+var2, false);
oHttp.send();
}
var1 and var2 are javascript variables or the custom elements that you want to post back