adjusted-box.js

function adjustedBoundingBox(boundingBox) {
  const overflowTop = Math.min(boundingBox.top, 0);
  const overflowLeft = Math.min(boundingBox.left, 0);
  const overflowRight = Math.min(window.innerWidth - boundingBox.right, 0);
  const overflowBottom = Math.min(window.innerHeight - boundingBox.bottom, 0);

  return {
    top: Math.max(boundingBox.top, 0),
    left: Math.max(boundingBox.left, 0),
    height: boundingBox.height + overflowTop + overflowBottom,
    width: boundingBox.width + overflowLeft + overflowRight
  };
}