Prototypal OOP

if (!Object.create) {
    Object.create = function (obj) {
        function f() { };
        f.prototype = obj;
        return new f();
    }
}

var Image = {
    init: function (title, thumbnailUrl, largeUrl) {
        this.title = title;
        this.thumbnailUrl = thumbnailUrl;
        this.largeUrl = largeUrl;
    }
};

var slider = (function () {
    var currentIndex = 0;
    var bigSlider = document.getElementById("big");
    var images = [];
    function add(image) {
        images.push(image);
    }
    function render() {
        var privBtn = document.getElementById("privBtn");
        privBtn.addEventListener("click", privBtnClick, false);
        var nextBtn = document.getElementById("nextBtn");
        nextBtn.addEventListener("click", nextBtnClick, false);

        bigSlider.setAttribute("src", images[0].largeUrl);
        var cont = document.getElementById("cont");
        cont.addEventListener("click", onClick, false);
        var documentFragmen = document.createDocumentFragment();
        for (index in images) {
            var img = document.createElement("img");
            img.setAttribute("src", images[index].thumbnailUrl);
            documentFragmen.appendChild(img);
        }
        cont.appendChild(documentFragmen);
    }
    function onClick(ev) {
        var elem = ev.target;
        var counter = 0;
        while(elem.previousElementSibling){
            counter++;
            elem = elem.previousElementSibling;
        }
        currentIndex = counter;
        bigSlider.setAttribute("src", images[currentIndex].largeUrl);
        //var urlArr = url.split("/");
        //var index = urlArr[urlArr.length - 1].substring(0, 1);
        //bigSlider = document.getElementById("big");
        //bigSlider.setAttribute("src", "image/" + index + "big.jpg")
    }
    function privBtnClick() {

        //var index = bigSlider.getAttribute("src").split("/")[1][0] | 0;
        currentIndex--;
        if (currentIndex < 0) {
            currentIndex = images.length - 1;
        }
        bigSlider.setAttribute("src", images[currentIndex].largeUrl);

    }
    function nextBtnClick() {
        //var index = bigSlider.getAttribute("src").split("/")[1][0] | 0;
        currentIndex++;
        if (currentIndex === images.length) {
            currentIndex = 0;
        }
        bigSlider.setAttribute("src", images[currentIndex].largeUrl);
    }
    return {
        add: add,
        render: render
    }
}());

var img1 = Object.create(Image);
img1.init("first", "image/1small.jpg", "image/1big.jpg");
slider.add(img1);

var img2 = Object.create(Image);
img2.init("second", "image/2small.jpg", "image/2big.jpg");
console.log(img2);
slider.add(img2);

var img3 = Object.create(Image);
img3.init("third", "image/3small.jpg", "image/3big.jpg");
slider.add(img3);

var img4 = Object.create(Image);
img4.init("fourth", "image/4small.jpg", "image/4big.jpg");
slider.add(img4);

var img5 = Object.create(Image);
img5.init("fifth", "image/5small.jpg", "image/5big.jpg");
slider.add(img5);

slider.render();