gistfile1.js

var currentlyIn = false; 
// we need somewhere to hold state so that we don't continuously emit events

$(window).bind('scroll', function() {
// bind the scroll event from the window so this function's called when the user scrolls
  var inView = ($(this).scrollTop() + $(this).height()) > $('.some-element').offset().top; 
  // check if the top of the element is less than the bottom of the window
  if (inView === currentlyIn) return true;
  // if the new state is the same as the old then don't do anything
  $('.some-element').trigger(inView ? 'in-view' : 'out-view');
  // 'else' trigger an event depending on whether the element has gone in or out of view
  currentlyIn = inView;
  // update the state
});