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: 200, // 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 : 10 // 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

  1 /*
  2  * Lazy Load - jQuery plugin for lazy loading images
  3  *
  4  * Version:  1.9.3
  5  *
  6  */
  7 
  8 (function($, window, document, undefined) {
  9     var $window = $(window);
 10 
 11     $.fn.lazyload = function(options) {
 12         var elements = this;
 13         var $container;
 14         var settings = {
 15             threshold       : 0,
 16             failure_limit   : 0,
 17             event           : "scroll",
 18             effect          : "show",
 19             container       : window,
 20             data_attribute  : "original",
 21             skip_invisible  : true,
 22             appear          : null,
 23             load            : null,
 24             placeholder     : "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAAAXNSR0IArs4c6QAAAARnQU1BAACxjwv8YQUAAAAJcEhZcwAADsQAAA7EAZUrDhsAAAANSURBVBhXYzh8+PB/AAffA0nNPuCLAAAAAElFTkSuQmCC"
 25         };
 26 
 27         function update() {
 28             var counter = 0;
 29 
 30             elements.each(function() {
 31                 var $this = $(this);
 32                 if (settings.skip_invisible && !$this.is(":visible")) {
 33                     return;
 34                 }
 35                 if ($.abovethetop(this, settings) ||
 36                     $.leftofbegin(this, settings)) {
 37                         /* Nothing. */
 38                 } else if (!$.belowthefold(this, settings) &&
 39                     !$.rightoffold(this, settings)) {
 40                         $this.trigger("appear");
 41                         /* if we found an image we'll load, reset the counter */
 42                         counter = 0;
 43                 } else {
 44                     if (++counter > settings.failure_limit) {
 45                         return false;
 46                     }
 47                 }
 48             });
 49 
 50         }
 51 
 52         if(options) {
 53             /* Maintain BC for a couple of versions. */
 54             if (undefined !== options.failurelimit) {
 55                 options.failure_limit = options.failurelimit;
 56                 delete options.failurelimit;
 57             }
 58             if (undefined !== options.effectspeed) {
 59                 options.effect_speed = options.effectspeed;
 60                 delete options.effectspeed;
 61             }
 62 
 63             $.extend(settings, options);
 64         }
 65 
 66         /* Cache container as jQuery as object. */
 67         $container = (settings.container === undefined ||
 68                       settings.container === window) ? $window : $(settings.container);
 69 
 70         /* Fire one scroll event per scroll. Not one scroll event per image. */
 71         if (0 === settings.event.indexOf("scroll")) {
 72             $container.bind(settings.event, function() {
 73                 return update();
 74             });
 75         }
 76 
 77         this.each(function() {
 78             var self = this;
 79             var $self = $(self);
 80 
 81             self.loaded = false;
 82 
 83             /* If no src attribute given use data:uri. */
 84             if ($self.attr("src") === undefined || $self.attr("src") === false) {
 85                 if ($self.is("img")) {
 86                     $self.attr("src", settings.placeholder);
 87                 }
 88             }
 89 
 90             /* When appear is triggered load original image. */
 91             $self.one("appear", function() {
 92                 if (!this.loaded) {
 93                     if (settings.appear) {
 94                         var elements_left = elements.length;
 95                         settings.appear.call(self, elements_left, settings);
 96                     }
 97                     $("<img />")
 98                         .bind("load", function() {
 99 
100                             var original = $self.attr("data-" + settings.data_attribute);
101                             $self.hide();
102                             if ($self.is("img")) {
103                                 $self.attr("src", original);
104                             } else {
105                                 $self.css("background-image", "url('" + original + "')");
106                             }
107                             $self[settings.effect](settings.effect_speed);
108 
109                             self.loaded = true;
110 
111                             /* Remove image from array so it is not looped next time. */
112                             var temp = $.grep(elements, function(element) {
113                                 return !element.loaded;
114                             });
115                             elements = $(temp);
116 
117                             if (settings.load) {
118                                 var elements_left = elements.length;
119                                 settings.load.call(self, elements_left, settings);
120                             }
121                         })
122                         .attr("src", $self.attr("data-" + settings.data_attribute));
123                 }
124             });
125 
126             /* When wanted event is triggered load original image */
127             /* by triggering appear.                              */
128             if (0 !== settings.event.indexOf("scroll")) {
129                 $self.bind(settings.event, function() {
130                     if (!self.loaded) {
131                         $self.trigger("appear");
132                     }
133                 });
134             }
135         });
136 
137         /* Check if something appears when window is resized. */
138         $window.bind("resize", function() {
139             update();
140         });
141 
142         /* With IOS5 force loading images when navigating with back button. */
143         /* Non optimal workaround. */
144         if ((/(?:iphone|ipod|ipad).*os 5/gi).test(navigator.appVersion)) {
145             $window.bind("pageshow", function(event) {
146                 if (event.originalEvent && event.originalEvent.persisted) {
147                     elements.each(function() {
148                         $(this).trigger("appear");
149                     });
150                 }
151             });
152         }
153 
154         /* Force initial check if images should appear. */
155         $(document).ready(function() {
156             update();
157         });
158 
159         return this;
160     };
161 
162     /* Convenience methods in jQuery namespace.           */
163     /* Use as  $.belowthefold(element, {threshold : 100, container : window}) */
164 
165     $.belowthefold = function(element, settings) {
166         var fold;
167 
168         if (settings.container === undefined || settings.container === window) {
169             fold = (window.innerHeight ? window.innerHeight : $window.height()) + $window.scrollTop();
170         } else {
171             fold = $(settings.container).offset().top + $(settings.container).height();
172         }
173 
174         return fold <= $(element).offset().top - settings.threshold;
175     };
176 
177     $.rightoffold = function(element, settings) {
178         var fold;
179 
180         if (settings.container === undefined || settings.container === window) {
181             fold = $window.width() + $window.scrollLeft();
182         } else {
183             fold = $(settings.container).offset().left + $(settings.container).width();
184         }
185 
186         return fold <= $(element).offset().left - settings.threshold;
187     };
188 
189     $.abovethetop = function(element, settings) {
190         var fold;
191 
192         if (settings.container === undefined || settings.container === window) {
193             fold = $window.scrollTop();
194         } else {
195             fold = $(settings.container).offset().top;
196         }
197 
198         return fold >= $(element).offset().top + settings.threshold  + $(element).height();
199     };
200 
201     $.leftofbegin = function(element, settings) {
202         var fold;
203 
204         if (settings.container === undefined || settings.container === window) {
205             fold = $window.scrollLeft();
206         } else {
207             fold = $(settings.container).offset().left;
208         }
209 
210         return fold >= $(element).offset().left + settings.threshold + $(element).width();
211     };
212 
213     $.inviewport = function(element, settings) {
214          return !$.rightoffold(element, settings) && !$.leftofbegin(element, settings) &&
215                 !$.belowthefold(element, settings) && !$.abovethetop(element, settings);
216      };
217 
218     /* Custom selectors for your convenience.   */
219     /* Use as $("img:below-the-fold").something() or */
220     /* $("img").filter(":below-the-fold").something() which is faster */
221 
222     $.extend($.expr[":"], {
223         "below-the-fold" : function(a) { return $.belowthefold(a, {threshold : 0}); },
224         "above-the-top"  : function(a) { return !$.belowthefold(a, {threshold : 0}); },
225         "right-of-screen": function(a) { return $.rightoffold(a, {threshold : 0}); },
226         "left-of-screen" : function(a) { return !$.rightoffold(a, {threshold : 0}); },
227         "in-viewport"    : function(a) { return $.inviewport(a, {threshold : 0}); },
228         /* Maintain BC for couple of versions. */
229         "above-the-fold" : function(a) { return !$.belowthefold(a, {threshold : 0}); },
230         "right-of-fold"  : function(a) { return $.rightoffold(a, {threshold : 0}); },
231         "left-of-fold"   : function(a) { return !$.rightoffold(a, {threshold : 0}); }
232     });
233 
234 })(jQuery, window, document);

posted @ 2017-03-05 15:55 haonanElva 阅读(1248) 评论(0) 编辑收藏举报

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jq图片懒加载

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