(function($) {
    
    $.belowthefold = function(element, settings) {
        var fold = $(window).height() + $(window).scrollTop();
        return fold <= $(element).offset().top - 0;
    };

    $.abovethetop = function(element, settings) {
        var top = $(window).scrollTop();
        return top >= $(element).offset().top + $(element).height() - 0;
    };

    $.rightofscreen = function(element, settings) {
        var fold = $(window).width() + $(window).scrollLeft();
        return fold <= $(element).offset().left - 0;
    };
    
    $.leftofscreen = function(element, settings) {
        var left = $(window).scrollLeft();
        return left >= $(element).offset().left + $(element).width() - 0;
    };
    
    $.inviewport = function(element, settings) {
        return !$.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);