56、用a标签实现点击下载

// 下载标注json
    download (data) {
      if (!data) {
        return
      }
      let blob = new Blob([data])
      let fileName = data.name
      if ('download' in document.createElement('a')) { // 不是IE浏览器
        let url = window.URL.createObjectURL(blob)
        let link = document.createElement('a')
        link.style.display = 'none'
        link.href = url
        link.setAttribute('download', fileName)
        document.body.appendChild(link)
        //设置下载文件的名字
        link.download = "班级二维码"
        link.click()
        document.body.removeChild(link) // 下载完成移除元素
        window.URL.revokeObjectURL(url) // 释放掉blob对象
      } else { // IE 10+
        window.navigator.msSaveBlob(blob, fileName)
      }
    }
```