Checking if DOM element is in view

gistfile1.txt

function isInView(element) {
  // set initial bounds
  var bounds = element.getBoundingClientRect();
  var left = bounds.left, top = bounds.top;
  var right = bounds.right, bottom = bounds.bottom;
  var currentElement = element;
  while (true) {
    if (!currentElement.offsetParent) {
      return false; // 'display: none;' not visible
    }
    // checking if any parent clips it
    for (var p = currentElement.parentElement; p; p = p.parentElement) {
      var parentBounds = p.getBoundingClientRect();
      // intersect
      left = Math.max(left, parentBounds.left);
      top = Math.max(top, parentBounds.top);
      right = Math.min(right, parentBounds.right);
      bottom = Math.min(bottom, parentBounds.bottom);
      if (left >= right || top >= bottom) {
        return false;
      }
    }
    // checking also parent window of the frame
    var defaultView = currentElement.ownerDocument.defaultView;
    var frameElement = defaultView.frameElement;
    if (!frameElement) {
      break; // no iframe parent, stopping
    }

    // fixing and cliping rect for the current window/view
    left -= defaultView.pageXOffset; right -= defaultView.pageXOffset;
    top -= defaultView.pageYOffset; bottom -= defaultView.pageYOffset;
    left = Math.max(0, left);
    top = Math.max(0, top);
    right = Math.min(defaultView.innerWidth, right);
    bottom = Math.min(defaultView.innerHeight, bottom);
    if (left >= right || top >= bottom) {
      return false;
    }

    // shifting to the frame coordinates and continue using iframe parents
    bounds = frameElement.getBoundingClientRect();
    left += bounds.left; right += bounds.left;
    top += bounds.top; bottom += bounds.top;    
    currentElement = frameElement;
  }
  return true;
}