How to change background-repeat and background-size by javascript

I currently have this and it's working for me:

<script type='text/javascript'>
            $(function () {
                var body = $('body');
                var backgrounds = [
                  'url(http://localhost:12448/css/images/back1.jpg) no-repeat',
                  'url(http://localhost:12448/css/images/back2.jpg) no-repeat'];
                var current = 0;

                function nextBackground() {
                    body.css(
                        'background',
                    backgrounds[current = ++current % backgrounds.length]);

                    setTimeout(nextBackground, 5000);
                }
                setTimeout(nextBackground, 5000);
                body.css('background', backgrounds[0]);               
            });
</script>

I need to implement also this part of css code in to my javascript, so i can get dynamically changing background and the same css settings as it changes:

body
    {
        background-image:           url('images/overlay.png'),      url('images/bg.jpg');
        background-repeat:          repeat,                         no-repeat;
        background-size:            auto,                           100% 100%;
    }

Can anyone help me with this?