check an element to see if it nears the bottom of the view port

isNearBottom.js

function isNearBottom(element, marginPx){
  marginPx = marginPx || 100;
  var elementOffsetTop = $(element).offset().top,
      nearBottomMargin = $(window).scrollTop() + $(window).height() - elementOffsetTop;
  return Math.abs(nearBottomMargin) <= marginPx;
}

It's useful for something like an accordion, when user clicks on a header at the bottom of the screen, it'd enhance user experience to scroll up the item and expand the content.