后台返回文件地址
window.location.href 只能下载单个文件,多个文件会被覆盖
function downFiles(){
let count=0;
let hiddenIFrameID = 'hiddenDownloader' + count++;
let iframe = document.createElement('iframe');
iframe.id = hiddenIFrameID;
iframe.style.display = 'none';
document.body.appendChild(iframe);
iframe.src = url;
}