求解释一下Jquery中图片预载入插件的原理

代码如下，谢谢<script type="text/javascript">/*the images preload plugin*/(function($) {$.fn.preload = function(options) {var opts = $.extend({}, $.fn.preload.defaults, options),o= $.meta ? $.extend({}, opts, this.data()) : opts;return this.each(function() {var $e= $(this),t= $e.attr(✀rel✀),i= $e.attr(✀href✀),l= 0;$(✀<img/>✀).load(function(i){++l;if(l==2) o.onComplete();}).attr(✀src✀,i);$(✀<img/>✀).load(function(i){++l;if(l==2) o.onComplete();}).attr(✀src✀,t);});};$.fn.preload.defaults = {onComplete: function(){return false;}};})(jQuery);</script>