(function($) { $.belowthefold = function(element, settings) { var fold = $(window).height() + $(window).scrollTop(); return fold <= $(element).offset().top - settings.threshold; }; $.abovethetop = function(element, settings) { var top = $(window).scrollTop(); return top >= $(element).offset().top + $(element).height() - settings.threshold; }; $.rightofscreen = function(element, settings) { var fold = $(window).width() + $(window).scrollLeft(); return fold <= $(element).offset().left - settings.threshold; }; $.leftofscreen = function(element, settings) { var left = $(window).scrollLeft(); return left >= $(element).offset().left + $(element).width() - settings.threshold; }; $.inviewport = function(element, settings) { return !$.rightofscreen(element, settings) && !$.leftofscreen(element, settings) && !$.belowthefold(element, settings) && !$.abovethetop(element, settings); }; $.extend($.expr[':'], { "below-the-fold": function(a, i, m) { return $.belowthefold(a, { threshold: 0 }); }, "above-the-top": function(a, i, m) { return $.abovethetop(a, { threshold: 0 }); }, "left-of-screen": function(a, i, m) { return $.leftofscreen(a, { threshold: 0 }); }, "right-of-screen": function(a, i, m) { return $.rightofscreen(a, { threshold: 0 }); }, "in-viewport": function(a, i, m) { return $.inviewport(a, { threshold: 0 }); } }); })(jQuery);