[获取滚动条宽度]通过offsetWidth

浏览器的异同没有统一的方法获取纵向或者横向滚动条的实际宽度

动态创建dom结构根据当前浏览器计算 纯在滚动条和不存在滚动条之间的 offsetWidth 差值

  const outer = document.createElement('div');
  outer.className = 'scrollbar__wrap';
  outer.style.visibility = 'hidden';
  outer.style.width = '100px';
  outer.style.position = 'absolute';
  outer.style.top = '-9999px';
  document.body.appendChild(outer);

  const widthNoScroll = outer.offsetWidth;
  outer.style.overflow = 'scroll';

  const inner = document.createElement('div');
  inner.style.width = '100%';
  outer.appendChild(inner);

  const widthWithScroll = inner.offsetWidth;
  outer.parentNode.removeChild(outer);

  return widthNoScroll - widthWithScroll;