slider.js

// slide bar framework utilized from https://www.w3schools.com/howto/howto_js_image_comparison.asp


function initComparisons() {
    var x, i;
    x = document.getElementsByClassName("img-comp-overlay");
    for (i = 0; i < x.length; i++) {
      compareImages(x[i]);
    }
    function compareImages(img) {
      var slider, img, clicked = 0, w, h;
      w = img.offsetWidth;
      h = img.offsetHeight;
      img.style.width = (w / 2) + "px";
      /*create slider:*/
      slider = document.createElement("DIV");
      slider.setAttribute("class", "img-comp-slider");
      /*insert slider*/
      img.parentElement.insertBefore(slider, img);
      /*position the slider in the middle:*/
      slider.style.top = (h / 2) - (slider.offsetHeight / 2) + "px";
      slider.style.left = (w / 2) - (slider.offsetWidth / 2) + "px";
      /*mouse interaction:*/
      slider.addEventListener("mousedown", slideReady);
      window.addEventListener("mouseup", slideFinish);
      slider.addEventListener("touchstart", slideReady);
      window.addEventListener("touchstop", slideFinish);
      function slideReady(e) {
        e.preventDefault();
        clicked = 1;
        /*execute a function when the slider is moved:*/
        window.addEventListener("mousemove", slideMove);
        window.addEventListener("touchmove", slideMove);
      }
      function slideFinish() {
        clicked = 0;
      }
      function slideMove(e) {
        var pos;
        if (clicked == 0) return false;
        pos = getCursorPos(e);
        if (pos < 0) pos = 0;
        if (pos > w) pos = w;
        slide(pos);
      }
      function getCursorPos(e) {
        var a, x = 0;
        e = e || window.event;
        a = img.getBoundingClientRect();
        x = e.pageX - a.left;
        x = x - window.pageXOffset;
        return x;
      }
      function slide(x) {
        /*resize the image:*/
        img.style.width = x + "px";
        /*position the slider:*/
        slider.style.left = img.offsetWidth - (slider.offsetWidth / 2) + "px";
      }
    }
  }