<script>
    var SlideShow = function (containerId, images) {

        // private members
        var self = this;
        var slides = images;
        var currentSlideIndex = 0;
        var container = document.getElementById(containerId);

        //private functions
        var getNextSlide = function() {
            if (currentSlideIndex < slides.length - 1)
                currentSlideIndex++;
            else
                currentSlideIndex = 0;

            return slides[currentSlideIndex];
        };

        var redraw = function() {
            var slide = getNextSlide();
            container.style.backgroundImage = "url('image/" + slide + "')";
        };


        // public functions
        self.initialize = function() {
            setInterval(redraw, 2000);
        }


    }

    document.addEventListener("DOMContentLoaded", function(event) {
        var show = new SlideShow('shadow', ['img_1.jpg', 'img_2.jpg', 'img_3.jpg']);
        show.initialize();
    });


</script>