add preload.js

src/main/app.ts

@@ -1,16 +1,19 @@
 import { app, BrowserWindow } from 'electron'
+import {join} from "path";
 
 function createWindow() {
     const win = new BrowserWindow({
         width: 800,
         height: 600,
         webPreferences: {
-            nodeIntegration: true
+            nodeIntegration: true,
+            preload: join(__dirname, 'preload.js')
         }
     })
 
     if (process.env.NODE_ENV === 'development') {
         win.loadURL('http://localhost:3000/')
+        win.webContents.openDevTools()
     } else {
         win.loadFile('dist/render/index.html')
     }