①截取文件名后缀

 <el-upload
     accept=".mdb"
     :limit="1"
     :auto-upload="false"
     :file-list="fileList"
     :show-file-list="false"
     class="upload-demo"
     action=""
     :on-change="handleChange"   // 文件发生变化时回调
 >
<div slot="tip" class="el-upload__tip">只能上传mdb文件</div>
</el-upload>

handleChange(file, fileLists) {
      // 截取文件名后缀
      let fileName = file.name;
      let pos = fileName.lastIndexOf(".");
      let lastName = fileName.substring(pos, fileName.length);
      if (lastName.toLowerCase() !== ".mdb") {
        this.$message.error("文件必须为.mdb类型");
        // 清空文件列表
        const newFileList = this.fileList.slice();
        newFileList.splice(0, 1);
        this.fileList = newFileList;
      } else { }

②简便法获取文件类型

 let fileType = fileList[0].name.replace(/.+\./, "")