Track mouse wheel events

mousewheel.js

document.addEventListener('mousewheel', function(e) {
  handleWheel(e);
}, false);

document.addEventListener('DOMMouseScroll', function(e) {
  .handleWheel(e);
}, false);


var handleWheel = function(e) {

  var delta = 0;
  if (e.wheelDelta) {

    delta = e.wheelDelta / 120;
    if (isOpera) {

      delta = -delta;
    }

  } else if (e.detail) {

    delta = -e.detail / 3;
  }



  if (delta > 0) {

    this.prev();
    return;
  }

  if (delta < 0) {

    this.next();
    return;
  }

};