gistfile1.js

(function () {
  (function (root, factory) {
    if (typeof define === 'function' && define.amd) {
      return define('jquery.in-viewport', ['jquery'], function ($) {
        return factory($, root);
      });
    } else {
      return factory(root.jQuery, root);
    }
  })(this, function($, window) {
    var $win = $(window);

    $.extend($.expr[':'], {
        "in-viewport": function (element) {
            var viewport = { top: $win.scrollTop()
                           , left : $win.scrollLeft()
                },
                $element = $(element),
                bounds = $element.offset();
                
            viewport.right = viewport.left + $win.width();
            viewport.bottom = viewport.top + $win.height();
            
            bounds.right = bounds.left + $element.outerWidth();
            bounds.bottom = bounds.top + $element.outerHeight();
            return (!(viewport.right < bounds.left || viewport.left > bounds.right || viewport.bottom < bounds.top || viewport.top > bounds.bottom));
        }
    });

    });
}).call(this);