js/jquery.onscreen.js


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// onScreen jQuery plugin v0.2.1
// (c) 2011 Ben Pickles
//
// http://benpickles.github.com/onScreen
//
// Released under MIT license.
;(function($) {
  $.expr[":"].onScreen = function(elem) {
    var $window = $(window)
    var viewport_top = $window.scrollTop()
    var viewport_height = $window.height()
    var viewport_bottom = viewport_top + viewport_height
    var $elem = $(elem)
    var top = $elem.offset().top
    var height = $elem.height()
    var bottom = top + height

    return (top >= viewport_top && top < viewport_bottom) ||
           (bottom > viewport_top && bottom <= viewport_bottom) ||
           (height > viewport_height && top <= viewport_top && bottom >= viewport_bottom)
  }
})(jQuery);