code: function detectDirType(dir, files) {
    var type, isIndexedFiles, isLengthMatched;
    type = 'object';
    isIndexedFiles = false;
    isLengthMatched = false;
    if (path.extname(dir) === '.array') {
      if (!files.length) {
        return 'array';
      }
      // double-check to see if its contents are Array-compatible
      isIndexedFiles = files.every(function (file) {
        var parts, index;
        parts = parseName(file);
        if (!parts.label || !(/^\d+$/).test(parts.label)) {
          return false;
        }
        index = parseInt(parts.label, 10);
        return index < files.length;
      });
      if (!isIndexedFiles) {
        return 'object';
      }
      files.sort(function (a, b) {
        return parseInt(a, 10) - parseInt(b, 10);
      });
      isLengthMatched =
        parseInt(files[files.length - 1], 10) === files.length - 1;
      if (isLengthMatched) {
        return 'array';
      }
    }
    return type;
  }
docs: caution: as a side-effect, this may sort the files Array
  @param {String} dir
  @param {String[]} files
  @ignore