js下载文件防止白屏

思路：用js创建一个iframe，让后指定src为下载目录。
var ifup = document.getElementById("ifup");
if(ifup)
{
    document.body.removeChild(ifup);
}
var elemIF = document.createElement("iframe");
elemIF.id='ifup';
elemIF.src =  tpri_dmp.root + '/process/Common_File?action=Common_Download&attachid=' + attachid + '&qt=1';
elemIF.style.display = "none";
document.body.appendChild(elemIF);