code: function createWritable() {
      var $args = arguments;return new Promise(function ($return, $error) {
          var file, ws;
          file = $args.length > 0 && $args[0] !== undefined ? $args[0] : getTempFile();
          return Promise.resolve(openFileForWrite(file)).then(function ($await_2) {
              try {
                  ws = $await_2;
                  return $return(ws);
              } catch ($boundEx) {
                  return $error($boundEx);
              }
          }.bind(this), $error);
      }.bind(this));
  }
docs: Open the file for writing and create a write stream.
  @param {string} ffile path to the file
  @returns {Promise<Writable>} A promise with the stream