//detect when thing is is viewport from scrolling up or down

HTML

<script src="//cdn.jsdelivr.net/jquery.waypoints/2.0.2/waypoints.min.js"></script>
<div class="thing"></div>
<div class="spacer"></div>
<div class="thing"></div>
<div class="spacer"></div>
<div class="thing"></div>
<div class="spacer"></div>
<div class="thing"></div>
<div class="spacer"></div>
<div class="thing"></div>
<div class="spacer"></div>

CSS

.thing {height:50px;background:#eaeaea;border:1px solid #ccc;}
.spacer {height:1000px;}

JavaScript

//detect when thing is is viewport from scrolling up or down
$('.thing').waypoint(function(down) {
  alert("thing in viewport down");
}, { offset: 'bottom-in-view' }); //sets alert when top of thing is at or enters bottom

$('.thing').waypoint(function(up) {
  alert("thing in viewport up");
}, { offset: 'bottom-in-view' }); //sets alert when top of thing is at or enters bottom

$.fn.waypoint.defaults = {
  context: window,
  continuous: true,
  enabled: true,
  horizontal: true,
  offset: 0, //sets default waypoint at top
  triggerOnce: false
}

//waypoint documentation - http://imakewebthings.com/jquery-waypoints/#doc-waypoint