Auto center pop up window

function PopupCenter() {
    var width = 600;
    var height = 480;
    var top = (screen.height / 2) - (height / 2);
    var left = (screen.width / 2) - (width / 2);

    var parametar = 'toolbar=no, location=no, directories=no, status=no, menubar=no, scrollbars=no, resizable=no, copyhistory=no, width=' + width + ', height=' + height + ', top=' + top + ', left=' + left;
    var url = 'Default.aspx'
    var windowName = 'Default';
    var targetWin = window.open(url, windowName, parametar);
    targetWin.focus();
    return false;
}

Page with query string

function PopupCenter(Name, Age) {
    var width = 600;
    var height = 480;
    var top = (screen.height / 2) - (height / 2);
    var left = (screen.width / 2) - (width / 2);

    var parametar = 'toolbar=no, location=no, directories=no, status=no, menubar=no, scrollbars=no, resizable=no, copyhistory=no, width=' + width + ', height=' + height + ', top=' + top + ', left=' + left;
    var url = 'Default.aspx?Name=' + Name + '&Age=' + Age;
    var windowName = 'Default';
    var targetWin = window.open(url, windowName, parametar);
    targetWin.focus();
    return false;
}

References
www.javascripter.net
msdn
htmlgoodies