Convert to TypeScript

Summary: Before looking into performance bottlenecks, I thought it wise to upgrade to TypeScript as that is where all plugins are heading

Reviewed By: jknoxville

Differential Revision: D18829689

fbshipit-source-id: 4c515f240d742f77e89f3cbdff500c69afb3ac06

src/utils/jsonTypes.tsx

@@ -0,0 +1,16 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @format
+ */
+
+export type JSON = JSONPrimitive | JSONArray | JSONObject;
+
+export type JSONPrimitive = null | boolean | number | string;
+
+export type JSONArray = JSON[];
+
+export type JSONObject = {[key: string]: JSON};