Set Popup in center of window

<script type="text/javascript">

        $(document).ready(function() {

            //select all the a tag with name equal to modal
            $('a[name=modal]').click(function(e) {
                //Cancel the link behavior
                e.preventDefault();

                //Get the A tag
                var id = $(this).attr('href');

                //Get the screen height and width
                var maskHeight = $(document).height();
                var maskWidth = $(window).width();

                //Set heigth and width to mask to fill up the whole screen
                $('#mask').css({ 'width': maskWidth, 'height': maskHeight });

                //transition effect       
                $('#mask').fadeIn(1000);
                $('#mask').fadeTo("slow", 0.8);

                //Get the window height and width
                var winH = $(window).height();
                var winW = $(window).width();

                //Set the popup window to center
                $(id).css('top', winH / 2 - $(id).height() / 2);
                $(id).css('left', winW / 2 - $(id).width() / 2);

                //transition effect
                $(id).fadeIn(2000);

            });

            //if close button is clicked
            $('.window .close').click(function(e) {
                //Cancel the link behavior
                e.preventDefault();

                $('#mask').hide();
                $('.window').hide();
            });

            //if mask is clicked
            // $('#mask').click(function() {
            //   $(this).hide();
            //   $('.window').hide();
            // });

            $(window).resize(function() {

                var box = $('#boxes .window');

                //Get the screen height and width
                var maskHeight = $(document).height();
                var maskWidth = $(window).width();
                //Set height and width to mask to fill up the whole screen
                $('#mask').css({ 'width': maskWidth, 'height': maskHeight });
                //Get the window height and width
                var winH = $(window).height();
                var winW = $(window).width();
                //Set the popup window to center
                box.css('top', winH / 2 - box.height() / 2);
                box.css('left', winW / 2 - box.width() / 2);

            });

        });

    </script>