/desktop-multiwindow-electron

name: desktop-multiwindow-electron
description: Multi-window management, WebContentsView, BaseWindow, window lifecycle, inter-window communication, state persistence

Electron Multi-Window Patterns

> **Quick Guide:** Use `BrowserWindow` for single-view windows. Use `BaseWindow` + `WebContentsView` for multi-view layouts (tabs, split panes, panels). `BrowserView` is deprecated since Electron 30 -- migrate to `WebContentsView`. Track windows with a `Map<string, BrowserWindow>` registry. Communicate between windows via the main process or `MessagePort` for direct renderer-to-renderer channels. Persist window bounds manually or use the upcoming `windowStatePersistence` API. Always close `webContents` explicitly when using `BaseWindow` -- unlike `BrowserWindow`, it does not auto-cleanup.

---

<critical_requirements>

CRITICAL: Before Using This Skill

**(You MUST close `webContents` explicitly when destroying a `BaseWindow` -- it does not auto-cleanup like `BrowserWindow`, causing memory leaks)**

**(You MUST use `WebContentsView` instead of `BrowserView` -- `BrowserView` is deprecated since Electron 30)**

**(You MUST route all inter-window communication through the main process or `MessagePort` -- never access another window's renderer directly)**

**(You MUST validate that saved window bounds are on a visible display before restoring -- monitors may disconnect between sessions)**

</critical_requirements>

---

**Auto-detection:** multi-window, BaseWindow, WebContentsView, BrowserView migration, contentView, addChildView, removeChildView, parent window, child window, modal window, window registry, MessagePort, MessageChannelMain, window state persistence, screen API, workArea, getAllDisplays, split view, tabs, panels, window lifecycle, ready-to-show, window-all-closed

**When to use:**

• Creating multi-view layouts (tabs, split panes, embedded panels) with BaseWindow + WebContentsView
• Managing multiple BrowserWindow instances with a window registry
• Migrating from deprecated BrowserView to WebContentsView
• Setting up parent/child or modal windows
• Communicating between windows (via main process relay or MessagePort)
• Persisting and restoring window position, size, and display state
• Placing windows on specific monitors using the screen API

**When NOT to use:**

• Single-window apps with one view (`BrowserWindow` is sufficient on its own)
• Choosing a UI framework for the renderer
• IPC patterns between main and a single renderer (basic IPC is outside multi-window scope)
• Styling or layout within a single renderer

**Key patterns covered:**

• BaseWindow + WebContentsView for multi-view layouts
• BrowserView to WebContentsView migration
• Window lifecycle events (ready-to-show, close, closed)
• Parent/child and modal windows
• Window registry with Map-based tracking
• Inter-window communication via main process and MessagePort
• Window state persistence (bounds, maximized, fullscreen)
• Multi-monitor placement with screen API

---

<philosophy>

Philosophy

Electron's window model has two tiers. **BrowserWindow** is the simple path: one window, one web view, automatic lifecycle management. **BaseWindow + WebContentsView** is the flexible path: one window shell containing multiple independently managed web views, each with its own renderer process and preload script.

The key architectural decision: **use BrowserWindow for single-view windows, BaseWindow for multi-view layouts.** BaseWindow trades convenience for control -- you manage view lifecycle, bounds, and cleanup explicitly.

**When to use BaseWindow + WebContentsView:**

• Tab bars, split editors, preview panels, embedded browser views
• Any layout where multiple independent web pages share one OS window
• Applications migrating from deprecated BrowserView

**When NOT to use BaseWindow:**

• Single-view windows (BrowserWindow is simpler and handles cleanup automatically)
• Windows that only need a toolbar or status bar (a single BrowserWindow with HTML layout is sufficient)

</philosophy>

---

<patterns>

Core Patterns

Pattern 1: BaseWindow with WebContentsView

BaseWindow is the window shell; WebContentsView instances are the content. Each view has its own renderer process and preload script.

const { BaseWindow, WebContentsView } = require("electron");

const win = new BaseWindow({ width: 1200, height: 800 });

const sidebar = new WebContentsView({
  webPreferences: { preload: path.join(__dirname, "preload.js") },
});
const main = new WebContentsView({
  webPreferences: { preload: path.join(__dirname, "preload.js") },
});

win.contentView.addChildView(sidebar);
win.contentView.addChildView(main);

const SIDEBAR_WIDTH = 250;
sidebar.setBounds({ x: 0, y: 0, width: SIDEBAR_WIDTH, height: 800 });
main.setBounds({ x: SIDEBAR_WIDTH, y: 0, width: 950, height: 800 });

sidebar.webContents.loadFile("sidebar.html");
main.webContents.loadFile("main.html");

**Key point:** Each WebContentsView needs its own `webPreferences` and preload script. BaseWindow has no `webContents` of its own. See [examples/core.md](examples/core.md) for complete split-view and tab examples with resize handling.

---

Pattern 2: BrowserView to WebContentsView Migration

BrowserView is deprecated since Electron 30. Migration is straightforward -- constructors have the same shape.

| Deprecated (BrowserView) | Replacement (WebContentsView) | | ---------------------------------------- | --------------------------------------------------------- | | `new BrowserView(opts)` | `new WebContentsView(opts)` | | `win.addBrowserView(view)` | `win.contentView.addChildView(view)` | | `win.removeBrowserView(view)` | `win.contentView.removeChildView(view)` | | `win.getBrowserViews()` | `win.contentView.children` | | `win.setT