base64位转化为文件，可以append

  handleSignUpload1() {
      let signBase64 = window.picBase64;
      let blob = this.dataURLtoFile(signBase64, "签字.jpg");
      console.log("blob", blob);
      let formData = new FormData();
      formData.append("webFile", blob);
      let loading = this.$ljLoading({
        lock: true,
        customClass: "loading-bc",
      });
      return this.sendRequest(
        "/oss-api-service/attachmentInfo/upload",
        formData
      )
        .then((res) => {
          loading.close();
          try {
            console.log("656", res);
            this.form.sign1.splice(0, 1, res.id);
            this.$message.success("签字成功");
          } catch (err) {
            console.log("err => ", err);
          }
        })
        .catch((err) => {
          loading.close();
        });
    },

dataURLtoFile(dataurl, filename) {
      let arr = dataurl.split(",");
      let mime = arr[0].match(/:(.*?);/)[1];
      let bstr = atob(arr[1]);
      let n = bstr.length;
      let u8arr = new Uint8Array(n);
      while (n--) {
        u8arr[n] = bstr.charCodeAt(n);
      }
      return new File([u8arr], filename, {
        type: mime,
      });
    },