Add url rewrite to serve files locally without requiring a server

src/index.js

@@ -1,4 +1,5 @@
-const { app, BrowserWindow } = require('electron')
+const { app, BrowserWindow, protocol, session } = require('electron')
+const path = require('path')
 
 function createWindow () {
   // Create the browser window.
@@ -17,8 +18,23 @@ function createWindow () {
 // This method will be called when Electron has finished
 // initialization and is ready to create browser windows.
 // Some APIs can only be used after this event occurs.
-app.whenReady().then(createWindow)
+app.whenReady().then(() => {
+  const root = path.normalize(`${__dirname}/..`)
 
+  // file:// interceptor to serve all assets without running a web server in the background
+  protocol.interceptFileProtocol('file', (request, callback) => {
+    let url = request.url.substr(7)    /* all urls start with 'file://' */
+    if(!url.startsWith(root)) {
+      if(url.startsWith('css/fonts') || url.startsWith('css/img')) {
+        url = url.substr(4)
+      }
+      url = path.normalize(`${root}/frontend/${url}`)
+    }
+    callback({ path: url})
+  })
+
+  createWindow()
+})
 // Quit when all windows are closed, except on macOS. There, it's common
 // for applications and their menu bar to stay active until the user quits
 // explicitly with Cmd + Q.