I would like suggestions about this structure in JS

Question

Good afternoon. Practicing a little, I decided to build a javascript slider, and chose to follow this construction line with a builder. The code is functional. However, I would like to encapsulate as much as possible the entire code structure. But I could not fit the following section inside the body of the object:

novoSlider.btnProx.onclick = function () {
    novoSlider.prox();
}
novoSlider.btnPrev.onclick = function () {
    novoSlider.prev();
}

Complete code:

<script>
    var sliderJs = function () {
        var elements = [];
        var pos = 0;
        var btnProx;
        var btnPrev;

        this.construtor = function (proxId, prevId, objJson) {
            this.btnProx = document.getElementById(proxId);
            this.btnPrev = document.getElementById(prevId);
            elements = objJson;
            container.childNodes[1].textContent = elements[pos].titulo;
            container.style.transition = "all .3s";
            container.style.backgroundImage = "url("+elements[pos].url+")";
        };

        this.prox = function () {
            if(pos != elements.length-1){
                pos = pos + 1;
                container.childNodes[1].textContent = elements[pos].titulo;
                container.style.backgroundImage = "url("+elements[pos].url+")";
            }else{
                pos = 0;
                container.childNodes[1].textContent = elements[pos].titulo;
                container.style.backgroundImage = "url("+elements[pos].url+")";
            }   
        };
        this.prev = function () {
            if(pos != 0){
                pos = pos -1;
                container.childNodes[1].textContent = elements[pos].titulo;
                container.style.backgroundImage = "url("+elements[pos].url+")";
            }else{
                pos = elements.length-1;
                container.childNodes[1].textContent = elements[pos].titulo;
                container.style.backgroundImage = "url("+elements[pos].url+")";
            }
        };
    };


    window.onload = function () {

        var objElements = [
            {titulo : "Jogador é demitido",
            url : "http://4.bp.blogspot.com/-Vp4z1HqcVWQ/VfcI2mUUjSI/AAAAAAAABMQ/t10j6_O6lEE/s300-c/infidelidade2.jpg" },
            {titulo : "Cunha abre processo de impeatchment",
            url : "http://www.atoananet.com.br/links/2015/08/11/artista-tranforma-fotos-aleatorias-em-divertidas-ilustracoes_300.jpg" },
            {titulo : "MegaSena acumulada", 
            url : "http://1.bp.blogspot.com/-8rt58bwMhTs/U_1SXIg8FSI/AAAAAAAAEMY/A3DZRYdMGSY/s300-c/cat01.jpg" }
        ];

        var novoSlider = new sliderJs();
        novoSlider.construtor("prox","ant",objElements);

        novoSlider.btnProx.onclick = function () {
            novoSlider.prox();
        }
        novoSlider.btnPrev.onclick = function () {
            novoSlider.prev();
        }
    }
</script>

Answer 1

From what I see in your code you can improve some things.

You don’t need this constructor logic. You can directly use these arguments when you call new sliderJs.

I joined the container as argument and removed some duplicate code...

 var sliderJs = function(proxId, prevId, elements, container) {
     var pos = 0;
     this.container = container;
     this.btnProx = document.getElementById(proxId);
     this.btnPrev = document.getElementById(prevId);
     this.container.childNodes[1].textContent = elements[pos].titulo;
     this.container.style.transition = "all .3s";
     this.container.style.backgroundImage = "url(" + elements[pos].url + ")";

     this.prox = function() {
         pos = pos != elements.length - 1 ? pos + 1 : 0;
         this.container.childNodes[1].textContent = elements[pos].titulo;
         this.container.style.backgroundImage = "url(" + elements[pos].url + ")";

     };
     this.prev = function() {
         pos = pos != 0 ? pos - 1 : elements.length - 1;
         this.container.childNodes[1].textContent = elements[pos].titulo;
         this.container.style.backgroundImage = "url(" + elements[pos].url + ")";
     };
     this.btnProx.addEventListener('click', this.prox);
     this.btnPrev.addEventListener('click', this.prev);
 };


 window.onload = function() {

     var objElements = [{
         titulo: "Jogador é demitido",
         url: "http://4.bp.blogspot.com/-Vp4z1HqcVWQ/VfcI2mUUjSI/AAAAAAAABMQ/t10j6_O6lEE/s300-c/infidelidade2.jpg"
     }, {
         titulo: "Cunha abre processo de impeatchment",
         url: "http://www.atoananet.com.br/links/2015/08/11/artista-tranforma-fotos-aleatorias-em-divertidas-ilustracoes_300.jpg"
     }, {
         titulo: "MegaSena acumulada",
         url: "http://1.bp.blogspot.com/-8rt58bwMhTs/U_1SXIg8FSI/AAAAAAAAEMY/A3DZRYdMGSY/s300-c/cat01.jpg"
     }];

     var novoSlider = new sliderJs("prox", "ant", objElements, document.getElementById('container'));
 }