function getBoundingClientRect(el) {
  var rect;

  try {
    rect = el.getBoundingClientRect();
  } catch (err) {
    // Ignore Windows 7 IE11 "Unspecified error"
    // https://github.com/w3c/IntersectionObserver/pull/205
  }

  if (!rect) return getEmptyRect();

  // Older IE
  if (!(rect.width && rect.height)) {
    rect = {
      top: rect.top,
      right: rect.right,
      bottom: rect.bottom,
      left: rect.left,
      width: rect.right - rect.left,
      height: rect.bottom - rect.top
    };
  }
  return rect;
}
Shims the native getBoundingClientRect for compatibility with older IE.
@param {Element} el The element whose bounding rect to get.
@return {Object} The (possibly shimmed) rect of the element.