<script>
function getFileType(fileName) {
  // 后缀获取
  let suffix = '';
  // 获取类型结果
  let result = '';
  try {
   const flieArr = fileName.split('.');
   suffix = flieArr[flieArr.length - 1];
  } catch (err) {
   suffix = '';
  }
  // fileName无后缀返回 false
  if (!suffix) { return false; }
  suffix = suffix.toLocaleLowerCase();
  // 图片格式
  const imglist = ['png', 'jpg', 'jpeg', 'bmp', 'gif'];
  // 进行图片匹配
  result = imglist.find(item => item === suffix);
  if (result) {
   return 'image';
  }
  // 匹配txt
  const txtlist = ['txt'];
  result = txtlist.find(item => item === suffix);
  if (result) {
   return 'txt';
  }
  // 匹配 excel
  const excelist = ['xls', 'xlsx'];
  result = excelist.find(item => item === suffix);
  if (result) {
   return 'excel';
  }
  // 匹配 word
  const wordlist = ['doc', 'docx'];
  result = wordlist.find(item => item === suffix);
  if (result) {
   return 'word';
  }
  // 匹配 pdf
  const pdflist = ['pdf'];
  result = pdflist.find(item => item === suffix);
  if (result) {
   return 'pdf';
  }
  // 匹配 ppt
  const pptlist = ['ppt', 'pptx'];
  result = pptlist.find(item => item === suffix);
  if (result) {
   return 'ppt';
  }
  // 匹配 视频
  const videolist = ['mp4', 'm2v', 'mkv', 'rmvb', 'wmv', 'avi', 'flv', 'mov', 'm4v'];
  result = videolist.find(item => item === suffix);
  if (result) {
   return 'video';
  }
  // 匹配 音频
  const radiolist = ['mp3', 'wav', 'wmv'];
  result = radiolist.find(item => item === suffix);
  if (result) {
   return 'radio';
  }
  // 其他 文件类型
  return 'other';
 }
console.log(getFileType("jb51.jpg"));
</script>