<img src="占位图" data-src="img/foot.jpg" />

;(function(){

    /*

    图片预加载

    @author liuming

    @demo $('img[data-src]').ImgLoading();

    */

    $.fn.ImgLoading=function(){

        var aImgs = [],/*缓存图片列表*/

            $win = $(window),

            img,imgTop,

            winH = $win.height(),

            Timmer=null,

            i,

            scrollTop;

        $.each($(this),function(){

            aImgs.push(this);

        });

        $win.bind('load scroll.ImgLoading',function(){

            if(Timmer){clearTimeout(Timmer);}

            Timmer = setTimeout(eachImg,100);

        });

        function eachImg(){

            /*数组为空 清除事件*/

            if(aImgs.length==0){return $win.unbind('scroll.ImgLoading');}

            scrollTop = $win.scrollTop();

            for(i=aImgs.length-1; i>-1; i--){

                img = $(aImgs[i]);

                imgTop = img.offset().top;

                /*判断图片正在屏幕中 */

                if(scrollTop+winH > imgTop && scrollTop<imgTop+winH){

                    img.attr('src',img.attr('data-src'));

                    aImgs.splice(i,1);

                }

            }

        }

    }

})();

$('img[data-src]').ImgLoading();