a标签下载图片，不要预览

const downloadhandler = () => {
    const link = document.createElement('a')
    // 这里是将url转成blob地址 将链接地址字符内容转变成blob地址
    fetch(icoUrl).then(res => res.blob()).then(blob => { 
      link.href = URL.createObjectURL(blob)
      link.download = icoData.data.download_file_path
      document.body.appendChild(link)
      link.click()
    })
  }