<div class="pbar">
 <div class="ui-widget-header" id="percent_bar" style="width: 23%;"></div>
 </div>

var fileCount=fileList.length();
 fileList.foreach(function(i,obj){
   ........//下载文件
  document.getElementById("percent_bar").style.width=i/fileCount*100 + "%";//改变内层div的宽度
 })

var i=0;
var fileCount=fileList.length();
var loop = function () {
 if(i>fileCount)//退出循环
　　return;
  .....//下载文件
  i++;
  document.getElementById("percent_bar").style.width=i/fileCount*100+"%";
　　　//下一步循环  that.loopId = window.setTimeout(loop, 0);7 }
that.loopId = window.setTimeout(loop, 0);