Introduction

tabs-broadcast is an open-source JavaScript library designed to facilitate seamless communication between browser tabs within a single application. It addresses a common challenge: how to synchronize state and events between multiple tabs without resorting to redundant server requests or complex workarounds. With this library, developers can establish message exchanges between tabs as if they were part of a single unified application, ensuring data consistency and resource optimization.

What problems does tabs-broadcast solve? In modern web applications, users often open the same page in multiple tabs. Without coordination, these tabs operate in isolation — they might duplicate expensive operations (such as fetching the same data), create conflicting states (for instance, showing different authentication statuses or settings), and increase the load on the server (due to multiple requests from the same user). The tabs-broadcast library provides a mechanism for centralized management in such scenarios. It allows one "main" tab to execute critical tasks (synchronizing with the server, fetching updates, writing to storage, etc.), while the other tabs simply receive the results and notifications. For developers, this means simpler code for tab synchronization without needing to manually handle low-level APIs.

Why is this useful? First, it enhances the user experience (UX): the user always sees the most current state across all open windows of the application. Second, it optimizes resources: by ensuring that heavy operations are executed only once, it reduces the browser’s load (fewer processes, connections, and timers) and lowers the server load (fewer duplicate requests). Third, it simplifies the development of features that require inter-tab communication (eliminating the need to reinvent the wheel with localStorage or postMessage). The library provides ready-to-use tools for registering event handlers and broadcasting messages, allowing you to focus on your application’s logic rather than on inter-tab intricacies.

Architectural Decisions

Under the hood, tabs-broadcast leverages the built-in browser API called BroadcastChannel — a mechanism for publishing and subscribing to messages between different contexts of the same origin (tabs, windows, iframes, or web workers). This library acts as an abstraction layer over the BroadcastChannel API, offering a higher-level interface with additional guarantees. Let’s explore the key architectural principles of tabs-broadcast:

1. Singleton Pattern.

The library implements a Singleton pattern as its entry point. This means that upon inclusion of tabs-broadcast, a single instance of the communication channel is created, to which all tabs of your application connect. No matter how many times you import and initialize tabs-broadcast across different tabs, under the hood only one named BroadcastChannel is used. This approach prevents the issues arising from multiple competing channels and ensures consistency — every tab “listens” to the same broadcast. Additionally, the Singleton pattern simplifies usage: the developer does not have to pass the instance around, simply calling the constructor in each tab, and the library will manage duplicate prevention automatically.

2. The "Primary and Secondary Tabs" Architecture.

A key innovation of tabs-broadcast over directly using the BroadcastChannel is the concept of designating one tab as Primary **(main) and the rest as **Secondary. When the library is initialized, one of the tabs is designated as the primary tab. This tab assumes the responsibility for executing exclusive tasks that require a single executor. All other tabs automatically become secondary — they do not duplicate the work but merely receive results and notifications from the primary. If the primary tab closes or refreshes, the library automatically assigns a new primary from among the remaining tabs —this happens transparently to both the user and the developer. This leader election protocol is implemented via BroadcastChannel: tabs exchange service messages to determine which one should become primary. For example, the first opened tab typically declares itself primary, and subsequent tabs learn about it through a broadcast signal. When the primary tab closes, it sends out a notification and one of the secondary tabs takes over the primary role. This selection protocol is embedded within tabs-broadcast and spares you from having to write such logic yourself.

3. Event-Driven (Pub/Sub) Model.

tabs-broadcast provides an interface for subscribing to events and broadcasting them. Internally, every event sent through the library is turned into a BroadcastChannel message with a specific event type (name) and accompanying data. All tabs subscribed to this event will receive the notification and can process it accordingly. Importantly, the library allows flexible configuration: you can choose to send messages from any tab (by default) or restrict it so that only the primary tab emits them. The latter option is useful for preventing conflicts — if you enable the emitByPrimaryOnly mode, then even if a secondary tab tries to emit an event, it will either be ignored or rerouted to the primary tab. This way, you can ensure that certain types of events originate only from one source. Additionally, the library supports the concept of layers —conditional channels within the channel: you can specify a layer name when sending or subscribing to an event, so that only listeners in that layer will receive the message. This helps structure the events (for example, separating events of different micro-frontends or modules) and enhances performance by filtering unnecessary handlers.

4. Resource Management.

The implementation of tabs-broadcast takes into account browser-specific nuances. For instance, on page unload (beforeunload event), it is recommended to close the communication channel to free up resources. The library provides a destroy() method which closes the BroadcastChannel and detaches the event listeners in the tab. This is considered good practice: although the browser will eventually clean up the connection when the tab closes, an explicit call to destroy() can help properly reassign the primary role in advance and finish necessary processes.

Why was this architecture chosen? The main goal is to ensure reliability and efficiency in inter-tab communication. Using the BroadcastChannel API provides rapid data exchange without needing server requests or local storage hacks; the primary/secondary tabs pattern prevents race conditions and duplication; and the event-driven model makes the library’s API familiar (similar to EventEmitter or an event bus). As a result, tabs-broadcast remains lightweight (a few hundred lines of code) and framework-agnostic, while addressing the important cases of synchronization. Such an architecture has proven its worth in scenarios where centralized state management across multiple open tabs is crucial.

Application Areas

Where can tabs-broadcast be applied? Let’s consider a few scenarios:

• Reactive Web Applications with Live Data.

If your application constantly receives real-time updates (e.g., currency exchange rates, stock prices, sports scores, social media feeds, chat messages, etc.) and users tend to open multiple tabs, the library allows you to synchronize these data. For example, a new message or chat notification received in one tab will instantly appear in all other tabs. Moreover, you can configure it so that only one tab maintains the server connection while the others receive updates through the BroadcastChannel, thus reducing network load.

• Single Page Applications (SPAs) and Micro-Frontends.

In large projects where the frontend is divided into separate micro-applications or multiple iframes are embedded in one window, inter-component communication is often required. tabs-broadcast can be used not only between tabs but also between windows and iframes (as long as they share the same domain). In this way, different parts of your application can communicate through a shared channel, for example, to notify all parts about a change in user settings or a theme update.

• Session and Authentication Synchronization.

The library is useful for managing authentication state across tabs. If a user logs out in one tab, you can immediately log them out in all other tabs by sending an appropriate event. Conversely, upon login or token refresh, the information can be disseminated instantly. This enhances security (ensuring no tab remains inadvertently logged in) and convenience (eliminating the need to manually refresh every tab).

• Exclusive Actions in a Single Instance.

Certain tasks are best executed by only one tab rather than in parallel across all open instances — for example, background synchronization with the server, periodic autosaving of drafts, playing background music/video, or displaying web push notifications. Using tabs-broadcast, you can guarantee that such actions occur only in one designated tab (the current primary). If the user switches to another tab, that tab becomes primary and continues the task. This prevents conflicts and redundant resource usage.

The library is especially beneficial in multi-window applications with high load and the need for data consistency. In cases where developers previously resorted to cumbersome workarounds (such as periodically polling the server from one tab and storing data in localStorage for others to read), now a few lines of code with tabs-broadcast suffice. Of course, keep in mind that the BroadcastChannel API is supported by modern browsers (Chrome, Firefox, Edge, Safari ≥ 14) and is not available in very old browsers like Internet Explorer. For projects that require legacy browser support, you might need a polyfill or an alternative approach. However, in most modern web applications, tabs-broadcast works out of the box.

Example Use-Case: A Streaming Platform with WebSocket Events

Let’s consider a practical scenario where tabs-broadcast shines. Imagine we are developing a streaming platform that delivers real-time events to users via WebSocket. This could be a live video streaming service with a real-time chat, a trading terminal updating stock prices, or a news portal with a live feed. The defining feature here is a constant flow of data from the server and the possibility of a user having many tabs open simultaneously. Without a coordinated approach, each tab would establish its own WebSocket connection to the server, receiving duplicate data and creating unnecessary load (both on the client and the server).

How does tabs-broadcast help? The idea is to have one WebSocket connection serve all tabs. This can be implemented as follows: the primary tab establishes the WebSocket connection and listens for new messages from the server. When an update arrives, the primary tab uses tabs-broadcast to relay the content of the message to all other tabs. The secondary tabs, upon receiving the event via the BroadcastChannel, update their UI (for example, appending a new chat message, refreshing viewer counts, or displaying a popup notification). As a result, even if a user has 5–10 tabs open, the server sees only one connection, while all tabs receive updates synchronously.

To implement this pattern, the code can be organized as follows:

import TabsBroadcast from 'tabs-broadcast';

// Initialize the communication between tabs
const tabs = new TabsBroadcast({
  onBecomePrimary: () => {
    // This callback is called when the current tab becomes the primary
    console.log("🌟 This tab is now the primary one");
    // Since this tab has just been designated as primary, open the WebSocket connection
    openWebSocket();
  },
  emitByPrimaryOnly: true  // Allow event emission only from the primary tab
});

// Function to establish the WebSocket connection (called only on the primary tab)
function openWebSocket() {
  const socket = new WebSocket('wss://streaming.example.com/updates');

  // Handler for messages from the server
  socket.addEventListener('message', (event) => {
    const data = JSON.parse(event.data);
    // Broadcast the received event to all tabs via tabs-broadcast
    tabs.emit('stream-update', data);
  });

  socket.addEventListener('open', () => {
    console.log('WebSocket connection established');
  });
  socket.addEventListener('close', () => {
    console.log('WebSocket connection closed');
  });
}

// Subscribe to stream update events in all tabs (both primary and secondary)
tabs.on('stream-update', (data) => {
  console.log('Stream update received:', data);
  // Update the UI of the current tab based on the new data
  renderUpdate(data);
});

// If the current tab is already primary when the page loads, open the WebSocket connection immediately
if (tabs.primary) {
  openWebSocket();
}

// Make sure to close the communication channel on page unload or refresh
window.addEventListener('beforeunload', () => {
  tabs.destroy();
});

In this example, the main logic is as follows:

• When the tab loads, we create an instance of TabsBroadcast. In the options, we pass the onBecomePrimary callback — which will execute when the tab becomes primary. Inside it, we call the function openWebSocket(), establishing the connection with the server. Thus, either immediately upon loading (if the tab is the first and primary) or later (if, for example, the primary tab was closed and the current tab is promoted) we open exactly one WebSocket connection.

• The option emitByPrimaryOnly: true ensures that only the primary tab can call tabs.emit(). We use this within the WebSocket message handler: when data is received from the server, tabs.emit('stream-update', data) is called, broadcasting the event to all subscribers.

• Then, in all tabs (including the primary), we subscribe to the 'stream-update' event using tabs.on('stream-update', ...). When the primary tab broadcasts the event, each tab executes the provided callback, for example, by calling renderUpdate(data) to update the UI (such as adding a new chat message or refreshing data).

• The check if (tabs.primary) { openWebSocket(); } is necessary so that in a tab that is already primary upon page load, the connection is opened immediately, without waiting for the onBecomePrimary event. This property, tabs.primary, is a boolean that tabs-broadcast sets to true for the primary tab.

• Finally, on page unload (beforeunload event), we call tabs.destroy(). This closes the BroadcastChannel for the tab. If the tab was primary, the remaining tabs will automatically select a new primary (which, in turn, will open a new WebSocket connection).

What happens "behind the scenes": as long as at least one tab with the application is open, one active WebSocket connection is maintained. All tabs are synchronized — the data is up to date, the user does not need to manually update anything. If he closes the tab through which the data went, the library seamlessly redirects the responsibilities to another tab. For the server, the user is still represented by a single connection, regardless of the number of tabs. This significantly reduces the load on the backend when scaling (for example, 1000 users with 5 tabs is equivalent to 1000 connections instead of 5000). The user's browser saves traffic and resources: there is no duplication of work on processing the same messages in several places.

In this example, the approach with tabs-broadcast significantly lightens the system load. In the context of the streaming platform, we obtain a scalable solution: regardless of how many tabs a user opens, the network traffic and load correspond to that of a single tab. Meanwhile, the user experience is improved — updates are received simultaneously and without lag across all tabs, thanks to the near-instantaneous BroadcastChannel (which operates locally with minimal delay).

Code and Examples

Let’s review the general usage of the tabs-broadcast library and best practices for its integration. Starting with the library is straightforward. It is distributed via npm, so first run the installation:

npm install tabs-broadcast

Then, include and initialize it in your application:

import TabsBroadcast from 'tabs-broadcast';

const tabs = new TabsBroadcast({
  channelName: 'my-app-channel',       // channel name (optional, default is 'tabs-broadcast')
  listenOwnChannel: false,            // whether to listen to events generated by this same tab
  emitByPrimaryOnly: false,           // whether to allow event emission only from the primary tab
  onBecomePrimary: (info) => {        // callback when this tab becomes primary
    console.log('This tab is now primary:', info);
  }
});

In this snippet we:

• Import the class TabsBroadcast from the package.
• Create an instance with options. You can omit parameters as they have default values. In this example, a custom channel name (my-app-channel) is specified, which is useful if multiple independent applications are running on the same domain and you want to separate their communications. The option listenOwnChannel: false means that the tab won’t receive its own emitted messages (this avoids handling duplicate events). The emitByPrimaryOnly: false is the default—if set to true, it restricts event emission to only the primary tab. Finally, onBecomePrimary defines a function that will execute when the current tab is promoted to primary. The object info (passed as part of the event’s detail) may contain additional data such as the tab identifier.

After initialization, you can subscribe to events and emit them. The API methods include:

• tabs.on(eventName, callback, [layer]) — subscribes to an event with the name eventName. Whenever any tab broadcasts such an event via the channel, the provided callback is executed in the current tab with the event data. Optionally, you can specify a layer (a string identifier), so that the handler only reacts to events within that layer. This method does not return a value. For example:

tabs.on('user-logout', () => {
  // Log the user out in this tab
  performLogout();
});

Here, when the 'user-logout' event is received (say, another tab initiated logout), the function performLogout() is called.

• tabs.emit(eventName, data, [layer]) — emits an event. It broadcasts a message with the name eventName and data data (which can be an object, string, or any serializable type) to all other tabs (and optionally to itself, if listenOwnChannel: true). If a layer is provided, only listeners in that same layer receive the message. This method respects the emitByPrimaryOnly setting. For example:

tabs.emit('new-notification', { text: 'Hello!' });

On a primary tab, this call will broadcast the event to all others, whereas on a secondary tab it may either do nothing (if emitByPrimaryOnly: true) or broadcast as well (if set to false). Typically, you’d generate events on the primary tab (as shown earlier) or universally, such as in the case of a local user action that needs to be propagated.

• tabs.off(eventName, callback) — unsubscribes from an event. Remove the handler if it’s no longer needed to avoid unnecessary calls.

• tabs.onList(listOfListeners) — a convenience method to register multiple events in one call. You pass an array where each element is a tuple [eventName, callback, layer] (with the layer being optional). It is equivalent to calling tabs.on for each event, but in a more concise format. This method is used, for instance, in the library’s demo browser for subscribing to multiple events at once.

• tabs.destroy() — tears down the channel. After calling this method, the current tab stops receiving messages and no longer participates in the synchronization. If this tab was primary, a new primary will be selected. It’s typically called before the page unloads.

Below is a short example demonstrating how to use these methods together and illustrating best practices:

// Initialize the channel
const tabs = new TabsBroadcast({
  onBecomePrimary: () => {
    console.log('🔑 I have become the primary tab.');
    startBackgroundSync(); // e.g., start a periodic background task
  },
  emitByPrimaryOnly: true
});

// Subscribe to a series of events at once
tabs.onList([
  ['settings-changed', (data) => applySettings(data)],   // apply new settings
  ['notify', (msg) => showNotification(msg), 'UI'],       // display a notification (only in the "UI" layer)
  ['logout', () => handleLogout()]                         // log out the user
]);

// ...later in your code, when the user changes settings:
function onUserChangedSettings(newSettings) {
  saveSettings(newSettings);
  tabs.emit('settings-changed', newSettings);
}

// ...upon receiving a push notification in the primary tab:
function onPushMessage(msg) {
  tabs.emit('notify', msg, 'UI');  // send notification to the "UI" layer
}

// Logout
function logoutAllTabs() {
  tabs.emit('logout');  // notify all tabs that a logout is required
  performLogout();      // also log out in the current tab
}

// Handle page unload
window.addEventListener('beforeunload', () => {
  tabs.destroy();
});

In this code snippet, you can see the best practices at work:

• Centralizing Background Tasks.
  In the example, when a tab becomes primary (via the onBecomePrimary callback), the function startBackgroundSync() is called to launch a background periodic task (e.g., polling the server). This task is run only in the primary tab. If the primary role shifts, the new primary will start the task accordingly, ensuring that background operations do not run concurrently in multiple tabs.

• Grouped Event Registration with onList.
  The example uses tabs.onList to subscribe to three different events in a single call, which makes the code cleaner. The use of layers is demonstrated with the 'notify' event that listens only in the "UI" layer. When tabs.emit('notify', msg, 'UI') is called, only handlers subscribed under "UI" receive the event, preventing unintended interception by other components.

• Broadcasting Changes and Commands.
  The function onUserChangedSettings calls tabs.emit('settings-changed', newSettings), informing all tabs about a settings update (for instance, a theme or language change). Each tab subscribed to 'settings-changed' then applies the changes via applySettings(data). Similarly, logoutAllTabs() demonstrates a global logout: an event 'logout' is broadcast, which every tab catches to execute handleLogout() (e.g., clearing tokens and redirecting to a login page). Note that we also call performLogout() immediately in the current tab to log out instantly — this redundancy can be adjusted based on your specific logic.

• Tearing Down Cleanly.
  As before, it is essential to call destroy() when the page is unloaded to detach from the channel, which helps in properly reassigning the primary role if necessary.

These examples demonstrate how easily you can integrate tabs-broadcast into your project. Essentially, just a few lines of code are required to initialize and then work with events in the familiar pattern. The library does not dictate your application’s structure — you decide which events to use and what data to pass. It only guarantees that when an event occurs in one tab, the others will know about it and can react accordingly.

Additional Materials

For a better understanding of how tabs-broadcast works, it’s useful to look at visual diagrams and code examples:

• The diagrams above compare the scenarios without and with tabs-broadcast in the context of WebSocket connections. They clearly show the performance and architectural gains.

• Check out the official demo application of the library: TabsBroadcast Demo. In the demo, you can open multiple tabs and click buttons that generate events. You will see how counters update synchronously across all tabs and how the "Primary" status is dynamically transferred when the current primary tab is closed. This live demonstration reinforces the concepts described in the article.

• It is beneficial to review the MDN documentation on the BroadcastChannel API to understand its low-level behavior. Knowing the underlying API helps during debugging or when extending the functionality — the library essentially wraps this API, adding role management and a friendly interface.

• If you’re interested in optimizing multiple tab scenarios further, consider reading about related approaches, such as using SharedWorker for shared tasks or the StorageEvent (triggered by changes in localStorage). There are insightful overviews on platforms like Habr that discuss various methods for synchronizing state across tabs. Essentially, tabs-broadcast implements one of the most efficient methods based on the BroadcastChannel API.

• For those who want to delve deeper, the library’s source code is available on GitHub. The code is written in TypeScript, well-structured, and commented. The repository also includes a Wiki and a CHANGELOG.md that detail technical nuances of the implementation.
  The diagrams, code examples, and referenced resources will help you better understand how tabs-broadcast achieves its goals and how you can apply it in real-world projects.

Conclusion

In summary, the tabs-broadcast library provides developers with a powerful tool for coordinating multiple browser tabs. It is particularly effective in scenarios where synchronization and consistency are critical — be it for real-time data updates, session management, or distributing workload between tabs. By using tabs-broadcast, you gain an out-of-the-box solution for several problems:

• Avoiding conflicts and duplication.
  Only one tab executes critical operations, preventing race conditions and parallel requests to the server.

• Resource optimization.
  Fewer active connections, timers, and background tasks translate into lower traffic, better battery performance (especially on mobile devices), and reduced server load.

• Simple synchronization.
  The event-driven model allows you to notify all tabs of an event in just a couple of lines of code. There’s no need to manually track open windows or resort to clumsy hacks — simply call tabs.emit().

Of course, every solution has its limitations. tabs-broadcast works only within the same domain (a limitation inherent to the BroadcastChannel API), and for older browsers you might need a polyfill or an alternative mechanism. It’s also worth noting that the terminology “primary/secondary” is conventional, and the library might evolve towards more neutral terms like “leader/follower.” In the future, the developers of tabs-broadcast might expand its functionality — for example, by adding an automatic fallback to localStorage in environments lacking BroadcastChannel support or integrating with Service Workers so that even after all tabs are closed the state can be preserved and resumed on a new session.

Nevertheless, as it stands, tabs-broadcast already addresses the intended use cases in most scenarios. It works excellently for SPAs and complex web applications where the user interacts through multiple windows simultaneously. If you need to synchronize state across tabs or distribute responsibilities among them, consider adopting this library. You will likely notice cleaner, more predictable code, and an improved user experience in multi-tab environments.

Why should you use tabs-broadcast?

Because it is a proactive step toward a better UX and more efficient code. The library handles the low-level work, providing an easy-to-use API that can be quickly mastered. Ultimately, everyone wins: developers enjoy a cleaner and more maintainable codebase, users benefit from a consistently behaving application, and DevOps/backend teams see reduced loads from duplicate requests.

In short, tabs-broadcast brings the concept of multi-threaded coordination into the front-end world, turning browser tabs into a cohesive “organism.” If your challenges involve state synchronization, session management, or load distribution among tabs, this library is definitely worth considering. Its use today leads to more responsive, reliable, and scalable web applications — and in the long run, such approaches might become the de facto standard in client-side architecture.

Useful links

• tabs-broadcast NPM library
• tabs-broadcast GitHub repo
• Broadcast Channel API MDN docs
• My website