vue 里面pdf下载，不是预览

   handleFileDownload: function (url, filename) {
       let a = document.createElement('a');
       a.href = url;
       a.download = filename;
       a.click();
   },
   handlePdfLink: function (filename, url) {
       filename = filename+".pdf"
       let that=this
       fetch(url, {
           method: 'get',
           responseType: 'arraybuffer',
       })
           .then(function (res) {
               if (res.status !== 200) {
                   return res.json()
               }
               return res.arrayBuffer()
           })
           .then((blobRes) => {
               // 生成 Blob 对象，设置 type 等信息
               const e = new Blob([blobRes], {
                   type: 'application/octet-stream',
                   'Content-Disposition': 'attachment'
               })
               // 将 Blob 对象转为 url
               const link = window.URL.createObjectURL(e)
               that.handleFileDownload(link, filename)
           }).catch(err => {
               console.error(err)
           })
   },