解决：js 根据图片链接（image url）下载，有的打开预览，有的下载

/**
     *  ### 适合预览操作的 Blob 类型，需要将链接地址字符内容转变成blob地址
          - image/png
          - image/jpeg
          - image/gif
          - audio/mpeg
          - audio/ogg
          - audio/wav
          - video/mp4
          - video/ogg
        ### 适合下载操作的 Blob 类型
          - text/plain
          - text/csv
          - application/pdf
          - application/json
          - application/xml
          - application/zip
          - application/octet-stream
     */
    async function downloadImg(url) {
      try {
        const res = await fetch(url);
        if (!res.ok) {
          throw new Error("fetch network response was not ok");
        }
        const blob = await res.blob();
        if (
          blob.type.includes("image") ||
          blob.type.includes("audio") ||
          blob.type.includes("video")
        ) {
          const a = document.createElement("a");
          a.href = URL.createObjectURL(blob);
          a.download = "";
          document.body.appendChild(a);
          a.click();
        } else {
          window.open(url);
        }
      } catch (error) {
        //有些图片url请求本身就出现了跨域等问题，目前纯前端本人还无解，只能直接open
        console.log("catcherror", err);
        window.open(url);
      }
    }