You can find the MIME type of any file in your Google Drive using getMimeType() method as long as the MIME is support by Google Drive. Your script can then easily figure out the actual type (more user friendly) of the file or document using the following getFileType method. For instance, Google Spreadsheet for application/vnd.google-apps.spreadsheet and so on.

var mimeType = file.getMimeType();
var fileType = getFileType(mimeType);

function getFileType(mimeType) {
  var filetype = '';

  switch (mimeType) {
    case MimeType.GOOGLE_APPS_SCRIPT:
      filetype = 'Google Apps Script';
      break;
    case MimeType.GOOGLE_DRAWINGS:
      filetype = 'Google Drawings';
      break;
    case MimeType.GOOGLE_DOCS:
      filetype = 'Google Docs';
      break;
    case MimeType.GOOGLE_FORMS:
      filetype = 'Google Forms';
      break;
    case MimeType.GOOGLE_SHEETS:
      filetype = 'Google Sheets';
      break;
    case MimeType.GOOGLE_SLIDES:
      filetype = 'Google Slides';
      break;
    case MimeType.FOLDER:
      filetype = 'Google Drive folder';
      break;
    case MimeType.BMP:
      filetype = 'BMP';
      break;
    case MimeType.GIF:
      filetype = 'GIF';
      break;
    case MimeType.JPEG:
      filetype = 'JPEG';
      break;
    case MimeType.PNG:
      filetype = 'PNG';
      break;
    case MimeType.SVG:
      filetype = 'SVG';
      break;
    case MimeType.PDF:
      filetype = 'PDF';
      break;
    case MimeType.CSS:
      filetype = 'CSS';
      break;
    case MimeType.CSV:
      filetype = 'CSV';
      break;
    case MimeType.HTML:
      filetype = 'HTML';
      break;
    case MimeType.JAVASCRIPT:
      filetype = 'JavaScript';
      break;
    case MimeType.PLAIN_TEXT:
      filetype = 'Plain Text';
      break;
    case MimeType.RTF:
      filetype = 'Rich Text';
      break;
    case MimeType.OPENDOCUMENT_GRAPHICS:
      filetype = 'OpenDocument Graphics';
      break;
    case MimeType.OPENDOCUMENT_PRESENTATION:
      filetype = 'OpenDocument Presentation';
      break;
    case MimeType.OPENDOCUMENT_SPREADSHEET:
      filetype = 'OpenDocument Spreadsheet';
      break;
    case MimeType.OPENDOCUMENT_TEXT:
      filetype = 'OpenDocument Word';
      break;
    case MimeType.MICROSOFT_EXCEL:
      filetype = 'Microsoft Excel';
      break;
    case MimeType.MICROSOFT_EXCEL_LEGACY:
      filetype = 'Microsoft Excel';
      break;
    case MimeType.MICROSOFT_POWERPOINT:
      filetype = 'Microsoft PowerPoint';
      break;
    case MimeType.MICROSOFT_POWERPOINT_LEGACY:
      filetype = 'Microsoft PowerPoint';
      break;
    case MimeType.MICROSOFT_WORD:
      filetype = 'Microsoft Word';
      break;
    case MimeType.MICROSOFT_WORD_LEGACY:
      filetype = 'Microsoft Word';
      break;
    case MimeType.ZIP:
      filetype = 'ZIP';
      break;
    default:
      filetype = 'Unknown';
  }

  return filetype;
}