diff --git a/src/components/App.js b/src/components/App.js
index 818c481..b696647 100644
--- a/src/components/App.js
+++ b/src/components/App.js
@@ -124,8 +124,8 @@ class App extends React.PureComponent<AppProps & Classes, AppState> {
       for (let i in topics) {
         const topic = topics[i];
         const stateTopic = this.topics[topic].state;
-        const parseVal = stateTopic ? stateTopic.type : null;
-        const val = parseVal == null ? message.toString() : parseVal(message);
+        const typeConversion = stateTopic?.type?.from ?? stateTopic?.type;
+        const val = (typeConversion ?? ((x) => x.toString()))(message);
         this.setMqttStateDebounced(
           {mqttState: Object.assign({},
             merge(this.state.mqttState, { [topic]: val}))});
@@ -145,16 +145,16 @@ class App extends React.PureComponent<AppProps & Classes, AppState> {
     this.setState({drawerOpened: false});
   }
 
-  changeState = (topic: string, value: string) => {
+  changeState = (topic: string, val: string) => {
     try {
-      if (this.topics[topic].command == null) {
+      const commandTopic = this.topics[topic].command;
+      if (commandTopic == null) {
         return;
       }
-      const rawTopic = this.topics[topic].command.name;
-      const transformValue = this.topics[topic].command.type;
-      const val =
-        transformValue == null ? value : transformValue(Buffer.from(value));
-      this.state.mqttSend(rawTopic, Buffer.from(val));
+      const rawTopic = commandTopic.name;
+      const typeConversion = commandTopic.type?.to ?? commandTopic.type;
+      const value = (typeConversion ?? Buffer.from)(val);
+      this.state.mqttSend(rawTopic, value);
     } catch (err) {
       this.setState({ error: err.toString() });
     }
diff --git a/src/components/ControlMap.js b/src/components/ControlMap.js
index 231dd1b..b723831 100644
--- a/src/components/ControlMap.js
+++ b/src/components/ControlMap.js
@@ -6,7 +6,9 @@ import map from "lodash/map";
 import filter from "lodash/filter";
 import reduce from "lodash/reduce";
 import MqttContext from "mqtt/context";
-import type { Controls, Control, UIControl, ControlUI } from "config/flowtypes";
+import type {
+  Controls, Control, UIControl, ControlUI, Layer
+} from "config/flowtypes";
 import { renderToString } from "react-dom/server";
 
 export type Point = [number, number];
diff --git a/src/config/flowtypes.js b/src/config/flowtypes.js
index be2091e..719b90b 100644
--- a/src/config/flowtypes.js
+++ b/src/config/flowtypes.js
@@ -1,16 +1,22 @@
 // @flow
 import type { Icon } from "config/icon";
 
-export type TopicType = (msg: Buffer) => string;
+export type TopicType = {
+  from: (msg: Buffer) => string,
+  to: (newstate: string) => Buffer
+};
 
-export type StateCommand = {
+export type StateTopicType = TopicType | ((msg: Buffer) => string);
+export type CommandTopicType = TopicType | ((newstate: string) => Buffer);
+
+export type StateCommand<T> = {
   name: string,
-  type: TopicType
+  type: T
 }
 
 export type Topic = {
-  state?: StateCommand,
-  command?: StateCommand,
+  state?: StateCommand<StateTopicType>,
+  command?: StateCommand<CommandTopicType>,
   defaultValue: string
 };
 export type Topics = Map<string, Topic>;
@@ -114,6 +120,17 @@ export type Space = {
   mqtt: string
 };
 
+export type Layer = {
+  image: string,
+  name: string,
+  baseLayer?: boolean,
+  defaultVisibility: "visible" | "hidden",
+  opacity?: number,
+  bounds: {
+    topLeft: Point,
+    bottomRight: Point
+  }
+};
 export type Config = {
   space: Space,
   topics: Topics | Array<Topics>,
diff --git a/src/config/types.js b/src/config/types.js
index 478108d..7cf4765 100644
--- a/src/config/types.js
+++ b/src/config/types.js
@@ -1,13 +1,22 @@
 // @flow
 import type { TopicType } from "config/flowtypes";
 import at from "lodash/at";
+import set from "lodash/set";
 
-export const string: TopicType = (msg: Buffer) => msg.toString();
+export const string: TopicType = {
+  from: (msg: Buffer) => msg.toString(),
+  to: (msg: string) => Buffer.from(msg)
+};
 
 export const json = (path: string, innerType?: TopicType): TopicType => {
-  const parseAgain = innerType == null ? (x) => x.toString() : innerType;
-  return (msg) => parseAgain(Buffer.from(
-    at(JSON.parse(msg.toString()), path)[0].toString()));
+  const parseAgain = innerType?.from ?? ((x) => x.toString());
+  const parseFirst = innerType?.to ?? ((x) => Buffer.from(x));
+  return {
+    from: (msg) => parseAgain(Buffer.from(
+      at(JSON.parse(msg.toString()), path)[0].toString())),
+    to: (msg) => Buffer.from(
+      JSON.serialize(set({}, path, parseFirst(msg).toString())))
+  };
 };
 
 export type TypeOptionParam = { otherwise?: string, [string]: string };
@@ -16,13 +25,17 @@ export const option = (values: TypeOptionParam): TopicType => {
     if (values.otherwise != null) {
       return values.otherwise;
     } else {
-      throw new Error(
-        `Value ${x.toString()} cannot be mapped by the option parameters given`
-      );
+      return x;
     }
   };
   const mapVal = (x) => (values[x] != null ? values[x] : defaultValue(x));
-  return (x) => mapVal(x.toString());
+  return {
+    from: (x) => mapVal(x.toString()),
+    to: (x) => Buffer.from(mapVal(x))
+  };
 };
 
-export const jsonArray = (msg: Buffer) => JSON.parse(msg.toString()).join(", ");
+export const jsonArray = {
+  from: (msg: Buffer) => JSON.parse(msg.toString()).join(", "),
+  to: (msg: string) => Buffer.from(`[${msg}]`)
+};
diff --git a/src/index.jsx b/src/index.jsx
index 60400b8..44740ce 100644
--- a/src/index.jsx
+++ b/src/index.jsx
@@ -1,7 +1,7 @@
 // @flow
 import "core-js/stable";
 import "regenerator-runtime/runtime";
-import "../node_modules/leaflet/dist/leaflet.css"
+import "../node_modules/leaflet/dist/leaflet.css";
 
 import React from "react";
 import ReactDOM from "react-dom";
diff --git a/types/types.js b/types/types.js
index 5503e1a..60d5691 100644
--- a/types/types.js
+++ b/types/types.js
@@ -10,15 +10,3 @@ declare type Classes = {
 declare type State = Map<string,string>;
 
 declare type Point = [number, number];
-
-declare type Layer = {
-  image: string,
-  name: string,
-  baseLayer?: boolean,
-  defaultVisibility: "visible" | "hidden",
-  opacity?: number,
-  bounds: {
-    topLeft: Point,
-    bottomRight: Point
-  }
-};
diff --git a/webpack.config.js b/webpack.config.js
index 89d6f9a..a2b9295 100644
--- a/webpack.config.js
+++ b/webpack.config.js
@@ -41,7 +41,13 @@ module.exports = env => ({
   },
   plugins: [
     new CleanWebpackPlugin(),
-    new WebpackShellPlugin({onBuildStart:preBuildScripts}),
+    new WebpackShellPlugin({
+      onBuildStart: {
+        scripts: preBuildScripts,
+        blocking: true,
+        parallel: false
+      }
+    }),
     new HtmlWebpackPlugin({
       title: 'Space Map',
       template: 'index.ejs'