jq图片懒加载

jQuery图片延迟加载插件jQuery.lazyload,使用延迟加载在可提高网页下载速度。在某些情况下，它也能帮助减轻服务器负载。

使用方法

引用jquery和jquery.lazyload.js到你的页面

<script src="jquery-1.11.0.min.js"></script>
<script src="jquery.lazyload.js?v=1.9.1"></script>

html图片调用方法

为图片加入样式lazy  图片路径引用方法用data-original

<img class="lazy" data-original="img/bmw_m1_hood.jpg">
<img class="lazy" data-original="img/bmw_m1_side.jpg">
<img class="lazy" data-original="img/viper_1.jpg">
<img class="lazy" data-original="img/viper_corner.jpg">
<img class="lazy" data-original="img/bmw_m3_gt.jpg">
<img class="lazy" data-original="img/corvette_pitstop.jpg">

js出始化lazyload并设置图片显示方式

<script type="text/javascript" charset="utf-8">
  $(function() {
      $("img.lazy").lazyload({effect: "fadeIn"});
  });
</script>

在图片中也可以不使用 class="lazy"，初始化时使用：

$("img").lazyload({effect: "fadeIn"});

这样就可以对全局的图片都有效！

参数设置

$("img.lazy").lazyload({
  placeholder : "img/grey.gif", //用图片提前占位
    // placeholder,值为某一图片路径.此图片用来占据将要加载的图片的位置,待图片加载时,占位图则会隐藏
  effect: "fadeIn", // 载入使用何种效果
    // effect(特效),值有show(直接显示),fadeIn(淡入),slideDown(下拉)等,常用fadeIn
  threshold: , // 提前开始加载
    // threshold,值为数字,代表页面高度.如设置为200,表示滚动条在离目标位置还有200的高度时就开始加载图片,可以做到不让用户察觉
  event: 'click',  // 事件触发时才加载
    // event,值有click(点击),mouseover(鼠标划过),sporty(运动的),foobar(…).可以实现鼠标莫过或点击图片才开始加载,后两个值未测试…
  container: $("#container"),  // 对某容器中的图片实现效果
    // container,值为某容器.lazyload默认在拉动浏览器滚动条时生效,这个参数可以让你在拉动某DIV的滚动条时依次加载其中的图片
  failurelimit :  // 图片排序混乱时
     // failurelimit,值为数字.lazyload默认在找到第一张不在可见区域里的图片时则不再继续加载,但当HTML容器混乱的时候可能出现可见区域内图片并没加载出来的情况,failurelimit意在加载N张可见区域外的图片,以避免出现这个问题.
});

懒加载jquery.lazyload.js  js代码为下边

 /*
  * Lazy Load - jQuery plugin for lazy loading images
  *
  * Version:  1.9.3
  *
  */

 (function($, window, document, undefined) {
     var $window = $(window);

     $.fn.lazyload = function(options) {
         var elements = this;
         var $container;
         var settings = {
             threshold       : ,
             failure_limit   : ,
             event           : "scroll",
             effect          : "show",
             container       : window,
             data_attribute  : "original",
             skip_invisible  : true,
             appear          : null,
             load            : null,
             placeholder     : "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAAAXNSR0IArs4c6QAAAARnQU1BAACxjwv8YQUAAAAJcEhZcwAADsQAAA7EAZUrDhsAAAANSURBVBhXYzh8+PB/AAffA0nNPuCLAAAAAElFTkSuQmCC"
         };

         function update() {
             var counter = ;

             elements.each(function() {
                 var $this = $(this);
                 if (settings.skip_invisible && !$this.is(":visible")) {
                     return;
                 }
                 if ($.abovethetop(this, settings) ||
                     $.leftofbegin(this, settings)) {
                         /* Nothing. */
                 } else if (!$.belowthefold(this, settings) &&
                     !$.rightoffold(this, settings)) {
                         $this.trigger("appear");
                         /* if we found an image we'll load, reset the counter */
                         counter = ;
                 } else {
                     if (++counter > settings.failure_limit) {
                         return false;
                     }
                 }
             });

         }

         if(options) {
             /* Maintain BC for a couple of versions. */
             if (undefined !== options.failurelimit) {
                 options.failure_limit = options.failurelimit;
                 delete options.failurelimit;
             }
             if (undefined !== options.effectspeed) {
                 options.effect_speed = options.effectspeed;
                 delete options.effectspeed;
             }

             $.extend(settings, options);
         }

         /* Cache container as jQuery as object. */
         $container = (settings.container === undefined ||
                       settings.container === window) ? $window : $(settings.container);

         /* Fire one scroll event per scroll. Not one scroll event per image. */
         if ( === settings.event.indexOf("scroll")) {
             $container.bind(settings.event, function() {
                 return update();
             });
         }

         this.each(function() {
             var self = this;
             var $self = $(self);

             self.loaded = false;

             /* If no src attribute given use data:uri. */
             if ($self.attr("src") === undefined || $self.attr("src") === false) {
                 if ($self.is("img")) {
                     $self.attr("src", settings.placeholder);
                 }
             }

             /* When appear is triggered load original image. */
             $self.one("appear", function() {
                 if (!this.loaded) {
                     if (settings.appear) {
                         var elements_left = elements.length;
                         settings.appear.call(self, elements_left, settings);
                     }
                     $("<img />")
                         .bind("load", function() {

                             var original = $self.attr("data-" + settings.data_attribute);
                             $self.hide();
                             if ($self.is("img")) {
                                 $self.attr("src", original);
                             } else {
                                 $self.css("background-image", "url('" + original + "')");
                             }
                             $self[settings.effect](settings.effect_speed);

                             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);
                             }
                         })
                         .attr("src", $self.attr("data-" + settings.data_attribute));
                 }
             });

             /* When wanted event is triggered load original image */
             /* by triggering appear.                              */
             if ( !== settings.event.indexOf("scroll")) {
                 $self.bind(settings.event, function() {
                     if (!self.loaded) {
                         $self.trigger("appear");
                     }
                 });
             }
         });

         /* Check if something appears when window is resized. */
         $window.bind("resize", function() {
             update();
         });

         /* With IOS5 force loading images when navigating with back button. */
         /* Non optimal workaround. */
         if ((/(?:iphone|ipod|ipad).*os /gi).test(navigator.appVersion)) {
             $window.bind("pageshow", function(event) {
                 if (event.originalEvent && event.originalEvent.persisted) {
                     elements.each(function() {
                         $(this).trigger("appear");
                     });
                 }
             });
         }

         /* Force initial check if images should appear. */
         $(document).ready(function() {
             update();
         });

         return this;
     };

     /* Convenience methods in jQuery namespace.           */
     /* Use as  $.belowthefold(element, {threshold : 100, container : window}) */

     $.belowthefold = function(element, settings) {
         var fold;

         if (settings.container === undefined || settings.container === window) {
             fold = (window.innerHeight ? window.innerHeight : $window.height()) + $window.scrollTop();
         } else {
             fold = $(settings.container).offset().top + $(settings.container).height();
         }

         return fold <= $(element).offset().top - settings.threshold;
     };

     $.rightoffold = function(element, settings) {
         var fold;

         if (settings.container === undefined || settings.container === window) {
             fold = $window.width() + $window.scrollLeft();
         } else {
             fold = $(settings.container).offset().left + $(settings.container).width();
         }

         return fold <= $(element).offset().left - settings.threshold;
     };

     $.abovethetop = function(element, settings) {
         var fold;

         if (settings.container === undefined || settings.container === window) {
             fold = $window.scrollTop();
         } else {
             fold = $(settings.container).offset().top;
         }

         return fold >= $(element).offset().top + settings.threshold  + $(element).height();
     };

     $.leftofbegin = function(element, settings) {
         var fold;

         if (settings.container === undefined || settings.container === window) {
             fold = $window.scrollLeft();
         } else {
             fold = $(settings.container).offset().left;
         }

         return fold >= $(element).offset().left + settings.threshold + $(element).width();
     };

     $.inviewport = function(element, settings) {
          return !$.rightoffold(element, settings) && !$.leftofbegin(element, settings) &&
                 !$.belowthefold(element, settings) && !$.abovethetop(element, settings);
      };

     /* Custom selectors for your convenience.   */
     /* Use as $("img:below-the-fold").something() or */
     /* $("img").filter(":below-the-fold").something() which is faster */

     $.extend($.expr[":"], {
         "below-the-fold" : function(a) { return $.belowthefold(a, {threshold : }); },
         "above-the-top"  : function(a) { return !$.belowthefold(a, {threshold : }); },
         "right-of-screen": function(a) { return $.rightoffold(a, {threshold : }); },
         "left-of-screen" : function(a) { return !$.rightoffold(a, {threshold : }); },
         "in-viewport"    : function(a) { return $.inviewport(a, {threshold : }); },
         /* Maintain BC for couple of versions. */
         "above-the-fold" : function(a) { return !$.belowthefold(a, {threshold : }); },
         "right-of-fold"  : function(a) { return $.rightoffold(a, {threshold : }); },
         "left-of-fold"   : function(a) { return !$.rightoffold(a, {threshold : }); }
     });

 })(jQuery, window, document);