Full blown example.

.gitignore

@@ -40,4 +40,6 @@ yarn-error.log*
 *.tsbuildinfo
 next-env.d.ts
 
-*.gbc
+*.gbc
+
+/data

public/emulator.html

@@ -66,7 +66,7 @@
       };
 
       const emulatorInit = data => {
-        EJS_gameUrl = data.game;
+        EJS_gameUrl = `/api/v1/rom?id=${data.gameId}`;
         EJS_core = data.core;
         EJS_gameName = data.gameName;
 
@@ -88,34 +88,35 @@
         }
 
         const { message } = data;
-
         switch(message) {
           case 'init':
             emulatorInit(data);
             break;
 
+          case 'volume':
+            EJS_emulator.setVolume(data.volume);
+            break;
+
           default:
             console.error('Unknown message', message);
         }
       };
 
-      EJS_ready = (...args) => {
-        send({ message: 'ready', data: args });
+      EJS_ready = () => {
+        send({ message: 'ready' });
       }
 
-      EJS_onSaveState = (...args) => {
-        send({ message: 'save', data: args });
+      EJS_onSaveState = () => {
+        send({ message: 'save' });
       }
 
-      EJS_onLoadState = (...args) => {
-        send({ message: 'load', data: args });
+      EJS_onLoadState = () => {
+        send({ message: 'load' });
       }
 
-      EJS_onGameStart = (...args) => {
-        send({ message: 'start', data: args });
+      EJS_onGameStart = () => {
+        send({ message: 'start' });
       }
-
     </script>
-    <!-- <script src="https://cdn.emulatorjs.org/stable/data/loader.js"></script> -->
   </body>
 </html>

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

src/pages/api/v1/rom.ts

@@ -0,0 +1,44 @@
+import { NextApiHandler } from "next";
+import * as fs from 'fs';
+import * as path from 'path';
+
+const PATH_ROMS = path.resolve('.', 'data', 'games');
+
+const handler:NextApiHandler = async (req, res) => {
+  if (req.method !== 'GET') {
+    res.setHeader('Allow', ['GET']);
+    res.status(405).end(`Method Not Allowed`);
+    return;
+  }
+
+  // ID query param
+  if(!req.query.id || typeof req.query.id !== 'string') {
+    res.status(404).end(`Not Found`);
+    return;
+  }
+
+  const { id } = req.query;
+  if(!id) {
+    res.status(404).end(`Not Found`);
+    return;
+  }
+
+  // Does rom exist?
+  const pathRom = path.resolve(PATH_ROMS, `${id}.bin`);
+  if(!fs.existsSync(pathRom)) {
+    res.status(404).end(`Not Found`);
+    return;
+  }
+
+  // Read rom
+  try {
+    const romStream = fs.createReadStream(pathRom);
+    res.setHeader('Content-Type', 'application/octet-stream');
+    res.setHeader('Content-Disposition', `attachment; filename="${id}.bin"`);
+    romStream.pipe(res);
+  } catch (error) {
+    res.status(500).end(`Internal Server Error`);
+  }
+};
+
+export default handler;

src/pages/games/[id]/play.tsx

@@ -26,7 +26,9 @@ export const Page:React.FC<PageProps> = ({ id }) => {
       <h1>Playing Game ID: {id}</h1>
       
       <div className={styles.play__emulator}>
-        <Emulator system='gbc' />
+        <Emulator
+          system='gbc'
+        />
       </div>
     </div>
   );