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
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
js出始化lazyload并设置图片显示方式
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 $("![]()
") 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);