//fileName是pdf名称 、filePath是pdf地址
downloadFile(fileName, filePath) { 
  var ajax = new XMLHttpRequest()
  ajax.open('GET', filePath, true)
  ajax.setRequestHeader('Cache-Control', 'no-cache')
  ajax.setRequestHeader('Access-Control-Allow-Origin', '*')
  ajax.responseType = 'blob'
  ajax.onload = (e) => {
    console.log(e)
    let res = e.target.response
    // let blob = new Blob([res],{type: "application/pdf;charset=UTF-8"}) // 这里的res为后端返回的流数据
    let blob = new Blob([res])
    let aLink = document.createElement('a')
    aLink.download = `${fileName}.pdf` // 下载文件的名字
    aLink.href = URL.createObjectURL(blob)
    aLink.click()
  }
  ajax.send()
},