Emits the output of the decoder as named events.
function Emitter(opts) {
  Transform.call(this);
  this._writableState.objectMode = true;
  this._readableState.objectMode = true;
  opts = opts || {};
  // emit a fixed event name
  // rather than the default type
  this.name = opts.name;

  this.passthrough = opts.passthrough;
}