Update main.js

Refer to preload.js

And some changes on whenReady for easier debugging

main.js

@@ -1,11 +1,15 @@
 // Importing modules
 const { app, BrowserWindow } = require('electron')
+const path = require('path')
 
 // Reusable function to instantiate windows
 const createWindow = () => {
     const win = new BrowserWindow({
         width: 800,
         height: 600,
+        webPreferences: {
+            preload: path.join(__dirname, 'preload.js'),
+        }
     })
 
     win.loadFile('index.html')
@@ -17,7 +21,9 @@ app.whenReady().then(() => {
 
     // Open a window if none are open (macos only)
     app.on('activate', () => {
-        if (BrowserWindow.getAllWindows().length === 0) createWindow()
+        if (BrowserWindow.getAllWindows().length === 0) {
+            createWindow()
+        }
     })
 })