code: function (source, fileExtension, globalOptions, beautify, callback) {
    var _this = this;
  
    if (globalOptions === null) {
      rcFile.for(this.resourcePath, function (err, path) {
        if (!err) {
          if (typeof path === "string") {
            _this.addDependency(path);
  
            fs.readFile(path, "utf8", function (err, file) {
              if (!err) {
                var options = getOptionsForExtension(JSON.parse(stripJsonComments(file)), fileExtension);
                callback(null, beautify(source, options));
              } else {
                callback(err);
              }
            });
          } else {
            callback(null, beautify(source, {}));
          }
        } else {
          callback(err);
        }
      });
    } else {
      callback(null, beautify(source, getOptionsForExtension(globalOptions, fileExtension)));
    }
  }
docs: Method parses file asynchronously
  @param {String} source        - file's content.
  @param {String} fileExtension - file's extension.
  @param {Object} globalOptions - configuration from weback file.
  @param {Function} callback    - callback function with processed file content or with error message.