使用ajax请求秒更新进度条

我认为这篇文章非常清楚 http://www.dave-bond.com/blog/2010/01/JQuery-ajax-progress-
HMTL5/

将其发布以供将来参考（应该删除博客）：

$.ajax({     xhr: function(){       var xhr = new window.XMLHttpRequest();       //Upload progress       xhr.upload.addEventListener("progress", function(evt){       if (evt.lengthComputable) {         var percentComplete = evt.loaded / evt.total;         //Do something with upload progress         console.log(percentComplete);         }       }, false);     //Download progress       xhr.addEventListener("progress", function(evt){         if (evt.lengthComputable) {var percentComplete = evt.loaded / evt.total;         //Do something with download progressconsole.log(percentComplete);         }       }, false);       return xhr;     },     type: 'POST',     url: "/",     data: {},     success: function(data){    //Do something success-ish    } });