[example] Improve preload bridge

- Enables only in devmode
- Generic port

example/main/preload.js

@@ -8,17 +8,23 @@ contextBridge.exposeInMainWorld("electron", {
   },
 });
 
-// Patch the global WebSocket constructor to use the correct DevServer url
+// Next.js Websocket DevServer is not listining on our custom scheme.
+// This is why we need to monkey patch the global WebSocket constructor
+// to use the correct DevServer url
 // More info: https://github.com/HaNdTriX/next-electron-server/issues/7
-webFrame.executeJavaScript(`Object.defineProperty(globalThis, 'WebSocket', {
-  value: new Proxy(WebSocket, {
-    construct: (Target, [url, protocols]) => {
-      if (url.endsWith('/_next/webpack-hmr')) {
-        // Fix the Next.js hmr client url
-        return new Target("ws://localhost:3000/_next/webpack-hmr", protocols)
-      } else {
-        return new Target(url, protocols)
+if (process.env.NEXT_ELECTON_SERVER_DEV === "true") {
+  webFrame.executeJavaScript(`Object.defineProperty(globalThis, 'WebSocket', {
+    value: new Proxy(WebSocket, {
+      construct: (Target, [url, protocols]) => {
+        if (url.endsWith('/_next/webpack-hmr')) {
+          // Fix the Next.js hmr client url
+          return new Target("ws://localhost:${
+            process.env.NEXT_ELECTON_SERVER_PORT || 3000
+          }/_next/webpack-hmr", protocols)
+        } else {
+          return new Target(url, protocols)
+        }
       }
-    }
-  })
-});`);
+    })
+  });`);
+}