Check if an element is visible [JavaScript]

We can find plenty of answers about how to check if an element is visible.

In my case the one which works with opacity, and into a scrollable area, is this one (that I have optimized):

function isScrolledIntoView(el, holder) {
  var bndElem = el.getBoundingClientRect();
  var bndHolder = holder.getBoundingClientRect();
  return bndElem.top <= bndHolder.top ? !(bndHolder.top - bndElem.top > bndElem.height) : !(bndElem.bottom - bndHolder.bottom > bndElem.height);
}