takazudo/dev-electron

Electron Development

Common Pattern: Thin Wrapper App

Electron as thin wrapper around a dev server (e.g., Vite, Docusaurus):

1. Show splash screen
2. Spawn dev server as background process
3. Wait for server ready
4. Show BrowserWindow pointing to localhost URL
5. Clean up server on quit

See references/background-process.md for implementation.

BrowserWindow Setup

Load the dev server URL directly in BrowserWindow (no webview, no tabs):

const { BrowserWindow, shell } = require("electron");

function createMainWindow(devServerUrl) {
  const win = new BrowserWindow({
    width: 1200,
    height: 800,
    title: "My App",
    show: false,
    webPreferences: {
      nodeIntegration: false,
      contextIsolation: true,
    },
  });

  win.loadURL(devServerUrl);
  win.once("ready-to-show", () => win.show());

  // Open external links in default browser
  const devServerOrigin = new URL(devServerUrl).origin;
  win.webContents.setWindowOpenHandler(({ url }) => {
    try {
      const parsed = new URL(url);
      if (parsed.protocol !== "http:" && parsed.protocol !== "https:") {
        return { action: "deny" };
      }
      if (parsed.origin !== devServerOrigin) {
        shell.openExternal(url);
        return { action: "deny" };
      }
    } catch {
      // Invalid URL
    }
    return { action: "deny" };
  });

  return win;
}

Key points:

• Use nodeIntegration: false + contextIsolation: true (secure defaults)
• Standard { role: "reload" } menu items work correctly (they reload the BrowserWindow content directly)
• No need for custom IPC, globalShortcut, or webview tags

Menu

Use standard Electron menu roles. No custom IPC needed:

const template = [
  {
    label: "View",
    submenu: [
      { role: "reload" },
      { role: "forceReload" },
      { role: "toggleDevTools" },
    ],
  },
  {
    label: "Edit",
    submenu: [
      { role: "undo" }, { role: "redo" },
      { type: "separator" },
      { role: "cut" }, { role: "copy" }, { role: "paste" },
      { role: "selectAll" },
    ],
  },
  {
    label: "Window",
    submenu: [
      { role: "minimize" },
      { role: "close" },
    ],
  },
];

Packaging & Build

electron-builder: Keep as devDependency (DO NOT use pnpm dlx)

electron-builder has 300+ sub-dependencies. Using pnpm dlx downloads them all on every invocation, making builds extremely slow. Always install it as a devDependency:

{
  "devDependencies": {
    "electron": "^35.7.5",
    "electron-builder": "^26.8.0"
  },
  "scripts": {
    "build": "electron-builder --mac",
    "build:dir": "electron-builder --mac --dir"
  }
}

Shared Modules: Use extraResources, NOT files glob

// WRONG - shared module won't be in the asar
"files": ["main.js", "../../../shared/module/**/*"]

// CORRECT - copies to app's Resources directory
"extraResources": [{ "from": "../../../shared/module", "to": "module" }]

Then resolve dynamically in main.js:

function getSharedCorePath() {
  if (app.isPackaged) {
    return path.join(process.resourcesPath, 'electron-app-core');
  }
  return path.join(__dirname, '..', '..', '..', 'shared', 'electron-app-core');
}

Dynamic Project Root (Don't Hardcode Paths)

Walk up from app.getPath("exe") checking each directory for package.json with the expected project name. This is robust against repo moves and directory restructuring — no fragile .. counting.

function findProjectRootFromExePath() {
  let dir = path.dirname(app.getPath("exe"));
  const root = path.parse(dir).root;
  while (dir !== root) {
    if (isProjectRoot(dir)) return dir;
    dir = path.dirname(dir);
  }
  return null;
}

See references/packaging.md for full pattern including isProjectRoot helper.

Critical Pitfalls

Open External Links in Default Browser (Cmd+Click)

Electron doesn't open links in the system browser by default. Use setWindowOpenHandler to intercept Cmd+click and route external URLs to the default browser via shell.openExternal. See BrowserWindow Setup above.

Validate URL protocol (allow only http: and https:) to prevent javascript: or other protocol injection.

Dev Server: Kill Stale Port Before Start

When the app crashes or is force-quit, the old dev server process may survive and hold the port. On next launch the new server can't bind, causing a timeout. Kill any existing process on the port before spawning:

const { execSync } = require("child_process");

function killProcessOnPort(port) {
  try {
    const output = execSync(`lsof -ti tcp:${port}`, { encoding: "utf-8" });
    const pids = output.trim().split("\n").filter(Boolean);
    for (const pid of pids) {
      process.kill(Number(pid), "SIGKILL");
    }
  } catch {
    // No process on port - fine
  }
}

Dev Server: Health Check Must Not Require HTTP 200

When the dev server framework uses a non-root baseUrl (e.g., Docusaurus with baseUrl: "/pj/app/doc/"), the root path / returns 404. Accept any HTTP response as proof the server is alive:

// WRONG - breaks when baseUrl is not "/"
(res) => resolve(res.statusCode === 200)

// CORRECT - any response means server is up
(res) => resolve(res.statusCode > 0)

Dev Server: Default URL Must Include baseUrl

When the framework uses a non-root baseUrl, the default URL must include the full path. Otherwise the app opens to a 404 page:

// WRONG - opens to 404 when baseUrl is "/pj/app/doc/"
const defaultUrl = "http://localhost:3000";

// CORRECT - include the full baseUrl path
const defaultUrl = "http://localhost:3000/pj/app/doc/";

Dev Server: Avoid Transient Errors During File Regeneration

When regenerating files that a running dev server watches, write new files before deleting stale ones. If you delete first, the dev server sees missing files and shows errors.

nodenv/anyenv PATH Issues

Spawned processes don't inherit version managers. Source shell profile first. See references/background-process.md.

Detailed References

• Packaging & build: references/packaging.md - pnpm dlx, extraResources, dynamic project root
• Background process & dev server: references/background-process.md - Spawn, wait, cleanup