Use React Context API

src/mqtt/context.js

@@ -0,0 +1,12 @@
+// @flow
+import React from "react";
+
+export type MqttContextValue = {
+  state: State,
+  changeState: (topic: string, value: string) => void
+};
+
+export default React.createContext({
+  state: {},
+  changeState: (_topic, _val) => {}
+});