JS没有通过触摸板平滑滚动

Question

我使用此代码使页面滚动顺畅。它适用于鼠标滚轮。但是使用触摸板滚动（用两根手指轻扫）表现得非常快。请帮忙解决这个问题。

小提琴：https://jsfiddle.net/EshanRajapakshe/faLmnygp/

JS代码：

new SmoothScroll();
function SmoothScroll(el) {
  var t = this, h = document.documentElement;
  el = el || window;
  t.rAF = false;
  t.target = 0;
  t.scroll = 0;
  t.animate = function() {
    t.scroll += (t.target - t.scroll) * 0.1;
    if (Math.abs(t.scroll.toFixed(5) - t.target) <= 0.47131) {
      cancelAnimationFrame(t.rAF);
      t.rAF = false;
    }
    if (el == window) scrollTo(0, t.scroll);
    else el.scrollTop = t.scroll;
    if (t.rAF) t.rAF = requestAnimationFrame(t.animate);
  };
  el.onmousewheel = function(e) {
    e.preventDefault();
    e.stopPropagation();
    var scrollEnd = (el == window) ? h.scrollHeight - h.clientHeight : el.scrollHeight - el.clientHeight;
    t.target += (e.wheelDelta > 0) ? -70 : 70;
    if (t.target < 0) t.target = 0;
    if (t.target > scrollEnd) t.target = scrollEnd;
    if (!t.rAF) t.rAF = requestAnimationFrame(t.animate);
  };
  el.onscroll = function() {
    if (t.rAF) return;
    t.target = (el == window) ? pageYOffset || h.scrollTop : el.scrollTop;
    t.scroll = t.target;
  };
}