packager: json reporter

Summary: The idea is to make it easier to interact with tools consuming the packager's output. For example, Nuclide. Do you think that'd work well?

Reviewed By: davidaurelio

Differential Revision: D4482041

fbshipit-source-id: 6c64d7963195a4d786ed8902640f9e9f279f5f83

packages/metro-bundler/react-packager/src/lib/JsonReporter.js

@@ -0,0 +1,30 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ * @flow
+ */
+
+'use strict';
+
+import {Writable} from 'stream';
+
+class JsonReporter<TEvent> {
+
+  _stream: Writable;
+
+  constructor(stream: Writable) {
+    this._stream = stream;
+  }
+
+  update(event: TEvent) {
+    this._stream.write(JSON.stringify(event) + '\n');
+  }
+
+}
+
+module.exports = JsonReporter;