JS: smaller lazy-load inspired by lazyload

gistfile1

(function($, window, document, undefined) {
    $.fn.lazyload = function(options) {
        var $window = $(window),
            elements = this,
            settings = {
                threshold       : 0,
                fadein_speed    : "200",
                container       : window,
                data_attribute  : "src",
                appear          : null,
                load            : null
            },
            containerIsWindow = settings.container === undefined || settings.container === window,
            $container = containerIsWindow ? $window : $(settings.container);

        if(options) $.extend(settings, options);

        function belowthefold(element, settings) {
            var fold;
            if (containerIsWindow) {
                fold = window.innerHeight + (window.pageYOffset || document.documentElement.scrollTop || document.body.scrollTop);
            } else {
                fold = $(settings.container).offset().top + $(settings.container).height();
            }
            return fold <= $(element).offset().top - settings.threshold;
        };
        function abovethetop(element, settings) {
            var fold;
            if (containerIsWindow) {
                fold = (window.pageYOffset || document.documentElement.scrollTop || document.body.scrollTop);
            } else {
                fold = $(settings.container).offset().top;
            }
            return fold >= $(element).offset().top + settings.threshold  + $(element).height();
        };
        function update() {
            elements.each(function() {
                var $this = $(this);
                if (abovethetop(this, settings)) {
                        /* Nothing. */
                } else if (!belowthefold(this, settings) ) {
                        $this.trigger("appear");
                }
            });
        };

        $container.bind("scroll", function() {
            return update();
        });
        $window
            .bind("resize", function() {
                update();
            })
            .load(function() {
                update();
            });

        if ((/iphone|ipod|ipad.*os 5/gi).test(navigator.appVersion)) {
            $window.bind("pageshow", function(event) {
                if (event.originalEvent.persisted) {
                    elements.each(function() {
                        $(this).trigger("appear");
                    });
                }
            });
        }

        return this.each(function() {
            var self = this,
                $self = $(self);
            self.loaded = false;
            $self
                .one("appear", function() {
                    if (!this.loaded) {
                        if (settings.appear) {
                            var elements_left = elements.length;
                            settings.appear.call(this, elements_left, settings);
                        }
                        var img = new Image,
                            src = $self.data(settings.data_attribute);
                        img.onload = function() {
                            $self
                                .css("opacity", .001)
                                .attr("src",src);
                            setTimeout(function() {
                                $self.animate({opacity: 1}, settings.fadein_speed);
                            }, 0);
                            self.loaded = true;
                            /* Remove image from array so it is not looped next time. */
                            var temp = $.grep(elements, function(element) {
                                return !element.loaded;
                            });
                            elements = $(temp);
                            if (settings.load) {
                                var elements_left = elements.length;
                                settings.load.call(self, elements_left, settings);
                            }
                        };
                        img.onerror = function() {
                            //Write your error handling code here.
                        };
                        img.src = src;//Consequently, this fires onload.
                    }
                })
                .bind("scroll", function() {
                    if (!self.loaded) $self.trigger("appear");
                });
        });
    };
})(jQuery, window, document);