Full blown example.

src/components/Emulator.tsx

@@ -9,35 +9,40 @@ type EmulatorCore = (
   'gambatte' | 'mgba'
 );
 
-const EMULATOR_SYSTEM_CORES:{ [key in EmulatorSystem]:EmulatorCore } = {
-  'gb': 'gambatte',
-  'gbc': 'gambatte',
-  'gba': 'mgba'
+type SendEmulatorMessageInit = {
+  message:'init';
+  core:EmulatorCore;
+  system:EmulatorSystem;
+  gameId:string;
+  gameName:string;
 }
 
+type SendEmulatorMessageVolume = {
+  message:'volume';
+  volume:number;
+};
+
+type SendEmulatorMessage = (
+  SendEmulatorMessageInit |
+  SendEmulatorMessageVolume
+);
+
+type ReceiveEmulatorMessage = (
+  { message: 'start' } |
+  { message: 'ready' } |
+  { message: 'save' } |
+  { message: 'load' }
+);
+
 export type EmulatorProps = {
   system:EmulatorSystem;
 };
 
-type SendEmulatorMessageInit = {
-  message:'init';
-  core:EmulatorCore;
-  system:EmulatorSystem;
-  game:string;
-  gameName:string;
-}
-
-type SendEmulatorMessage = (
-  SendEmulatorMessageInit
-);
-
-type ReceiveEmulatorOnGameStart = {
-  message:'start'
-}
-
-type ReceiveEmulatorMessage = (
-  ReceiveEmulatorOnGameStart
-);
+const EMULATOR_SYSTEM_CORES:{ [key in EmulatorSystem]:EmulatorCore } = {
+  'gb': 'gambatte',
+  'gbc': 'gambatte',
+  'gba': 'mgba'
+};
 
 export const Emulator:React.FC<EmulatorProps> = props => {
   const iframeRef = useRef<HTMLIFrameElement>(null);
@@ -55,7 +60,7 @@ export const Emulator:React.FC<EmulatorProps> = props => {
       message: 'init',
       core: EMULATOR_SYSTEM_CORES[props.system],
       system: props.system,
-      game: '/test.gbc',
+      gameId: '0',
       gameName: 'Pokemon - Crystal Version'
     });
 
@@ -66,12 +71,12 @@ export const Emulator:React.FC<EmulatorProps> = props => {
       }
       
       const msg = e.data as ReceiveEmulatorMessage;
-      console.log('recv', msg);
       switch(msg.message) {
         case 'start':
-          console.log('Game started!');
-          break
-
+        case 'ready':
+        case 'load':
+        case 'save':
+          break;
         default:
           console.error('Invalid message received:', msg);
           break