图片延迟加载实现

(function($) {
    $.fn.lazyload = function(options) {
        var settings = {
            threshold: 0,
            failurelimit: 0,
            event: "scroll",
            effect: "show",//默认效果为show
            container: window
        };
        if (options) {
            $.extend(settings, options);
        }
        var elements = this;


        if ("scroll" == settings.event) {
            $(settings.container).bind("scroll", function(event) {
                var counter = 0;
                elements.each(function() {

                    if ($.abovethetop(this, settings) ||
                        $.leftofbegin(this, settings)
                        ) {
                        self.loaded = false;
                    }
                    else if (!$.belowthefold(this, settings) &&
                        !$.rightoffold(this, settings)) {
                        self.loaded = false;
                        $(this).trigger("appear");
                    }
                    else {
                        self.loaded = true;
                        if (counter++ > settings.failurelimit) {
                            return false;
                        }
                    }
                });

                var temp = $.grep(elements, function(element) {
                    return !element.loaded;
                });
                elements = $(temp);
            });
        }



        this.each(function() {
            var self = this;
    
            if (settings.placeholder) {
            $(self).attr("src", settings.placeholder);
            } 

 

            $(self).one("appear", function() {
                if (!this.loaded) {
                    $("<img />")
                        .bind("load", function() {
                            $(self)
                                .hide()
                                .attr("src", $(self).attr("original"))
                                [settings.effect](settings.effectspeed);
                            self.loaded = true;
                        })
                        .attr("src", $(self).attr("original"));
                };
            });

            if ("scroll" != settings.event) {
                $(self).bind(settings.event, function(event) {
                    if (!self.loaded) {
                        $(self).trigger("appear");
                    }
                });
            }
        });
        $(settings.container).trigger(settings.event);
        return this;

    };

 

    $.belowthefold = function(element, settings) {
        if (settings.container === undefined || settings.container === window) {
            var fold = $(window).height() + $(window).scrollTop();
        } else {
            var fold = $(settings.container).offset().top + $(settings.container).height();
        }
        return fold <= $(element).offset().top - settings.threshold;
    };

    $.rightoffold = function(element, settings) {
        if (settings.container === undefined || settings.container === window) {
            var fold = $(window).width() + $(window).scrollLeft();
        } else {
            var fold = $(settings.container).offset().left + $(settings.container).width();
        }
        return fold <= $(element).offset().left - settings.threshold;
    };

    $.abovethetop = function(element, settings) {
        if (settings.container === undefined || settings.container === window) {
            var fold = $(window).scrollTop();
        } else {
            var fold = $(settings.container).offset().top;
        }
        return fold >= $(element).offset().top + settings.threshold + $(element).height();
    };

    $.leftofbegin = function(element, settings) {
        if (settings.container === undefined || settings.container === window) {
            var fold = $(window).scrollLeft();
        } else {
            var fold = $(settings.container).offset().left;
        }
        return fold >= $(element).offset().left + settings.threshold + $(element).width();
    };

 

    $.extend($.expr[‘:‘], {
        "below-the-fold": "$.belowthefold(a, {threshold : 0, container: window})",
        "above-the-fold": "!$.belowthefold(a, {threshold : 0, container: window})",
        "right-of-fold": "$.rightoffold(a, {threshold : 0, container: window})",
        "left-of-fold": "!$.rightoffold(a, {threshold : 0, container: window})"
    });
})(jQuery);

 

(function($) {
    $.fn.lazyload = function(options) {
        var settings = {
            threshold: 0,
            failurelimit: 0,
            event: "scroll",
            effect: "show",
            container: window,
            original: "original",
            firstCount: 10, //第一次加载数量
            everyCount: 3,   //以后每次加载
            moveScrollTop: 100//每次移动多少像素加载
        };
        if (options) {
            $.extend(settings, options);
        }
        var elements = this;
        var self = this;
        var count = 0;
        if (settings.placeholder) {
            $(self).attr("src", settings.placeholder);
        }
        for (i = 0; i < settings.firstCount; i++) {
            var trueSrc = $(elements[i]).attr(settings.original);
            $(elements[i]).attr("src", trueSrc);
            $(elements[i]).attr(settings.original, "finish");

        }
        $(window).scroll(function() { 
            elements = $("img@[" + settings.original + "!=‘finish‘]"); //获取未加载图片集
            var i = 0;
            for (i = 0; i < settings.everyCount; i++) {
                var trueSrc = $(elements[i]).attr(settings.original);

                $(elements[i]).hide().attr("src", trueSrc)[settings.effect](settings.effectspeed);
                
                
               // $(elements[i]).attr("src", trueSrc);
                $(elements[i]).attr(settings.original, "finish");
                if (elements.length == 0) {
                    $(window).unbind("scroll");
                };
            }
            count++;
        });
        return false;
    };
})(jQuery);