efficient JS Snippet used to be warned when a DOM element is about to be seen by the user, for progressive enhancement and performance boost. Dependancies on jQuery (you have it) and underscore.js (you really should have it)
Usage
<div id="taking-space">Scroll down ↓</div>
<div id="container">Should not see me</div>
<script>
window.onAreaVisible(
$('#container'), // that DOM element will be enhanced only when visible
function() {
// scope is window
// no arguments given
// here goes your init method
$('#container').html('enhanced DOM element')
},
100 // run the method 100 pixel before seeing the element
);
</script>