A minimalist jQuery plugin to add triggers for elements entering or leaving the browser viewport. Even on touch devices.

That's it. Just two triggers. Do with it what you will.

Initialize on elements via .inviewtoo with a selector of your choice. Then use bind() or on() to subscribe your super custom function to the inview and/or leftview events.

<script src="//code.jquery.com/jquery-latest.min.js"></script>
<script src="/path/to/jquery-inviewtoo.min.js"></script>
<script type="text/javascript">
  $(document).ready(function() {
  
    $('#my_element').inviewtoo()
      .bind('inview',function(){
        console.log('Now you see me');
      })
      .bind('leftview',function(){
        console.log('Now you do not');
      });
  
  });
</script>

You can pass in the following options to tailor the triggers to your needs:

edge_threshold (Default: 250)

Number of pixels outside the viewport to "pad" element visibility calculations with.

debounce (Default: 250)

Number of miliseconds to suspend (in|left)view triggers after completion. This delay will debounce viewport changes to allow smooth changes, especially when users are mercilessly swiping across large pages on touchscreen devices.

context (Default: window)

The DOM context in which to calculate element visibility. Genearlly safe to leave to default.

Example

$('#my_element').inviewtoo({edge_threshold:500,debounce:100,context:'#my_area'})
  .bind('inview',function(){
    console.log('Now you see me');
  });

The mechanics of this plugin use basic ECMAScript calls and simple math. It should be highly compatible and unlikely to break in the near future.

Tested with:

• Chrome 13+
• IE 6+
• Firefox 4+
• Safari 4+

The touchend event has been tested on iPad 1-3, iPhone 3-4S and Android 1.6-4.1 to properly trigger when the viewport changes.

Many other "Lazy Load" style javascript plugins.

• The quintessential jQuery LazyLoad
• PixelTango's Bullseye

Bullseye is great, but I wanted the context to bind to a single refresh function with a quick local array for watched elements.

Another tricky thing was dealing with triggers firing too often. Eventually these resources on Debouncing the viewport calculation smoothed things out.

• Ben "Cowboy" Alman's excellent Throttle and Debounce
• Which led to a classic Unscriptable post on Javascript Debounce
• Ajaxian's very simple approach won out