通过a标签，下载图片

代码

    // 图片下载
    onDownload(filepath, filename) {
      const x = new XMLHttpRequest()
      x.open('GET', filepath, true)
      x.responseType = 'blob'
      x.onload = function () {
        const blob = x.response
        const url = window.URL.createObjectURL(blob)
        // 判断是否是IE浏览器
        if (window.navigator.msSaveBlob) {
          try {
            window.navigator.msSaveBlob(blob, filename)
          } catch (e) {
          }
        } else {
          const a = document.createElement('a')
          a.href = url
          a.download = filename
          a.click()
        }
      }
      x.send()
    },