web性能优化之- 自定义函数延迟触发 jquery插件

今天碰到一个很奇快的需求，大致如下：html页面有很多div容器，每个div容器的数据都是通过ajax请求来处理的。一般情况处理ajax请都在windows的load事件中，由于页面的div容器太多造成windows的load事件中ajax请求太多；所以我们只需要处理那些在浏览器中看得见的div容器。假如我们现在有10个div容器，每个屏幕刚好显示1个div容器，如果我们放到windows的load事件中，那么刚开始就有10个ajax请求。其实用户可能根本不会看到后面几个div容器，所以我们通过这个插件来延迟这些ajax的请求，刚加载页面有1个或2个ajax请求，当滚动条滚到相应div的时候，div再发起ajax请求。

jquery.lazyevent.js插件源代码:

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

 $.fn.lazyevent = function (options) {
 var elements = this;
 var settings = {
 threshold: 0,
 event: "scroll",
 container: window,
 skip_invisible: true,
 fn: null,
 data: null
 };
 function update() {
 var counter = 0;

 elements.each(function () {
 var $this = $(this);
 if (settings.skip_invisible && !$this.is(":visible")) {
 return;
 }
 /* if (!belowthefold(this, settings) && !rightoffold(this, settings)) {
 $this.trigger("fire");
 }*/
 if (inviewport(this, settings)) {
 $this.trigger("fire");
 }
 });

 }
 if (options) {
 $.extend(settings, options);
 }
 var $container = (settings.container === undefined || settings.container === window) ? $window : $(settings.container);

 if (0 === settings.event.indexOf("scroll")) {
 $container.bind(settings.event, function (event) { return update(); });
 }
 this.each(function () {
 var self = this;
 var $self = $(self);
 self.fired = false;
 $self.one("fire", function () {
 if (!this.fired) {
 if (settings.fn) {
 settings.fn.call(self, settings.data);
 }
 self.fired = true;
 var temp = $.grep(elements, function (element) { return !element.fired; });
 elements = $(temp);
 }
 });

 if (0 !== settings.event.indexOf("scroll")) {
 $self.bind(settings.event, function (event) {
 if (!self.fired) {
 $self.trigger("fire");
 }
 });
 }
 });

 $window.bind("resize", function (event) {
 update();
 });


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

 if (settings.container === undefined || settings.container === window) {
 fold = $window.height() + $window.scrollTop();
 } else {
 fold = $container.offset().top + $container.height();
 }
 return fold <= $(element).offset().top - settings.threshold;
 };

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

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

 return fold <= $(element).offset().left - settings.threshold;
 };
 var abovethetop = function (element, settings) {
 var fold;

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

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

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

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

 return fold >= $(element).offset().left + settings.threshold + $(element).width();
 };
 var inviewport = function (element, settings) {
 return !abovethetop(element, settings) && !leftofbegin(element, settings) &&
 !belowthefold(element, settings) && !rightoffold(element, settings);

 };
 update();
 return this;
 };

})(jQuery, window);

jquery.lazyevent..min.js代码：

(function(a,c){var b=a(c);a.fn.lazyevent=function(j){var g=this;var l={threshold:0,event:"scroll",container:c,skip_invisible:true,fn:null,data:null};function m(){var n=0;g.each(function(){var o=a(this);if(l.skip_invisible&&!o.is(":visible")){return}if(h(this,l)){o.trigger("fire")}})}if(j){a.extend(l,j)}var d=(l.container===undefined||l.container===c)?b:a(l.container);if(0===l.event.indexOf("scroll")){d.bind(l.event,function(n){return m()})}this.each(function(){var o=this;var n=a(o);o.fired=false;n.one("fire",function(){if(!this.fired){if(l.fn){l.fn.call(o,l.data)}o.fired=true;var p=a.grep(g,function(q){return !q.fired});g=a(p)}});if(0!==l.event.indexOf("scroll")){n.bind(l.event,function(p){if(!o.fired){n.trigger("fire")}})}});b.bind("resize",function(n){m()});var f=function(n,p){var o;if(p.container===undefined||p.container===c){o=b.height()+b.scrollTop()}else{o=d.offset().top+d.height()}return o<=a(n).offset().top-p.threshold};var k=function(n,p){var o;if(p.container===undefined||p.container===c){o=b.width()+b.scrollLeft()}else{o=d.offset().left+d.width()}return o<=a(n).offset().left-p.threshold};var e=function(n,p){var o;if(p.container===undefined||p.container===c){o=b.scrollTop()}else{o=d.offset().top}return o>=a(n).offset().top+p.threshold+a(n).height()};var i=function(n,p){var o;if(p.container===undefined||p.container===c){o=b.scrollLeft()}else{o=d.offset().left}return o>=a(n).offset().left+p.threshold+a(n).width()};var h=function(n,o){return !e(n,o)&&!i(n,o)&&!f(n,o)&&!k(n,o)};m();return this}})(jQuery,window);

html调用代码：

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
 <title>lazyevent</title>
 <script type="text/javascript" src="Scripts/jquery-1.7.js"></script>
 <script type="text/javascript" src="Scripts/jquery.lazyevent.js"></script>
 <style type="text/css">
 /* .test
 {
 height: 500px;
 display: inline-block;
 width: 4000px;
 }
 .test div
 {
 float: left;
 }
 */.test div
 {
 width: 500px;
 height: 500px;
 }
 </style>
</head>
<body>
 <div style="height: 200px">
 </div>
 <div class="test">
 <div style="background-color: Green">
 Green</div>
 <div style="background-color: Lime">
 Lime</div>
 <div style="background-color: Maroon; display:none">
 Maroon</div>
 <div style="background-color: Olive">
 Olive</div>
 <div style="background-color: Red; display: none">
 Red</div>
 <div style="background-color: ButtonFace">
 ButtonFace</div>
 <div style="background-color: Aqua">
 Aqua</div>
 <div style="background-color: AppWorkspace">
 AppWorkspace</div>
 </div>
 <script type="text/javascript">
 $(function () {
 $(".test div").lazyevent({
 data: "hello word",
 fn: function (data) {
 var html = $(this).html();
 alert(data + ":" + html);
 }
 });
 });
 </script>
</body>
</html>