jquery实现异步加载图片（懒加载图片一种方式）

 (function($) { 
        // alert($.fn.scrollLoading); 
        $.fn.scrollLoading = function(options) { 
          var defaults = { 
            attr: "data-url" 
          }; 
          var params = $.extend({}, defaults, options || {}); 
          params.cache = []; 
          $(this).each(function() { 
            var node = this.nodeName.toLowerCase(), 
              url = $(this).attr(params["attr"]); 
            if(!url) { 
              return; 
            } 
            var data = { 
              obj: $(this), 
              tag: node, 
              url: url 
            }; 
            params.cache.push(data); 
          }); 
 
          var loading = function() { 
            var st = $(window).scrollTop(), 
              sth = st + $(window).height(); 
            $.each(params.cache, function(i, data) { 
              var o = data.obj, 
                tag = data.tag, 
                url = data.url; 
              if(o) { 
                post = o.position().top; 
                posb = post + o.height(); 
                if((post > st && post < sth) || (posb > st && posb < sth)) { 
                  if(tag === "img") { 
                    o.attr("src", url); 
                  } else { 
                    o.load(url); 
                  } 
                  data.obj = null; 
                } 
              } 
            }); 
            return false; 
          }; 
 
          loading(); 
          $(window).bind("scroll", loading); 
        }; 
      })(jQuery);

 $(document).ready(function () { 
    //实现图片慢慢浮现出来的效果 
    $("img").load(function () { 
      //图片默认隐藏  
      $(this).hide(); 
      //使用fadeIn特效  
      $(this).fadeIn("5000"); 
    }); 
    // 异步加载图片，实现逐屏加载图片 
    $(".scrollLoading").scrollLoading();  
  });