Micro Frontends Architecture with Module Federation · Lesson

Custom Communication Solutions

Design and implement custom communication mechanisms tailored to specific Micro Frontend needs.

Custom Communication Solutions is a free Micro Frontends Architecture with Module Federation lesson on CoddyKit — lesson 3 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Micro Frontends Architecture with Module Federation learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Beyond Standard Communication

In Micro Frontend architectures, communication between different parts is crucial. We've explored event buses and shared state management.

However, sometimes your specific needs might call for more tailored approaches. This lesson dives into designing and implementing custom communication solutions.

Why Custom Solutions?

Why would you choose a custom solution over an established pattern?

Specific Interaction: When a very particular, direct interaction is needed.
Performance: To optimize for very high-frequency or low-latency communication.
Minimal Overhead: For simple, ad-hoc needs without bringing in heavy libraries.
Tight Coupling (Rare): In scenarios where two MFEs are intentionally very close and share a parent context.

Direct Callback Passing

One custom approach involves passing functions (callbacks) directly from a host application to a remote application as props or arguments. This is suitable when a host component directly renders a remote component and needs to react to its actions.

Module Federation allows you to share functions just like components or data.

Example: Passing a Callback

Imagine a host passing a 'notify' function to a remote, which then calls it. This is a simplified JavaScript representation:

function hostApp() {
  function handleNotification(message) {
    console.log(`Host received: ${message}`);
  }

  // In a real MFE, remote would be loaded
  // and `onNotify` passed as a prop.
  // For demo, we'll simulate the call.
  console.log("Host ready to receive.");
  remoteApp(handleNotification);
}

function remoteApp(onNotify) {
  console.log("Remote app started.");
  setTimeout(() => {
    onNotify("Data processed successfully!");
  }, 1000);
}

hostApp();

Browser's postMessage API

The postMessage API is a powerful browser feature for secure cross-origin communication between windows, iframes, and Web Workers.

It's ideal for sending messages between a host and an embedded MFE (e.g., in an iframe) where direct JavaScript access is restricted due to security policies.

Example: postMessage (Conceptual)

This is how a host and remote (e.g., in an iframe) would conceptually use postMessage to communicate. Note: This requires a browser environment to run fully.

// Host (parent window):
// const iframe = document.getElementById('remote-mfe');
// iframe.contentWindow.postMessage('Hello from Host!', 'http://remote.com');
// window.addEventListener('message', (event) => {
//   if (event.origin === 'http://remote.com') {
//     console.log('Host received:', event.data);
//   }
// });

// Remote (inside iframe):
// window.addEventListener('message', (event) => {
//   if (event.origin === 'http://host.com') {
//     console.log('Remote received:', event.data);
//     event.source.postMessage('Hello from Remote!', event.origin);
//   }
// });

// This snippet simulates the message flow:
function simulatePostMessage() {
  console.log("Simulating postMessage...");
  const hostMessage = "Hello from Host!";
  const remoteMessage = "Hello from Remote!";

  // Host sends to Remote
  console.log(`Host sends: "${hostMessage}"`);

  // Remote receives and replies
  console.log(`Remote receives: "${hostMessage}"`);
  console.log(`Remote sends: "${remoteMessage}"`);

  // Host receives reply
  console.log(`Host receives: "${remoteMessage}"`);
}

simulatePostMessage();

Shared Global Registry/Service

For specific, limited global data or services, you can create a custom JavaScript object or class and expose it via Module Federation's shared scope.

This acts like a lightweight, custom singleton that all federated applications can access and interact with, without full state management.

Example: Custom Shared Registry

Here's a simple custom registry object that could be shared. Each MFE could import and use mySharedRegistry.

// mySharedRegistry.js (exposed via Module Federation)
const mySharedRegistry = {
  _data: {},
  set: function(key, value) {
    this._data[key] = value;
    console.log(`Registry updated: ${key} = ${value}`);
  },
  get: function(key) {
    return this._data[key];
  },
  getAll: function() {
    return { ...this._data };
  }
};

// Simulate usage in different MFEs
console.log("--- MFE A ---");
mySharedRegistry.set("userTheme", "dark");

console.log("--- MFE B ---");
console.log(`Current user theme: ${mySharedRegistry.get("userTheme")}`);
mySharedRegistry.set("appVersion", "1.0.1");

console.log("--- MFE A (again) ---");
console.log(`Current app version: ${mySharedRegistry.get("appVersion")}`);

Considerations & Trade-offs

While custom solutions offer flexibility, they come with trade-offs:

Increased Coupling: Can make MFEs less independent.
Complexity: Harder to maintain and debug compared to standard patterns.
Scalability: May not scale well if communication needs grow.
Security: `postMessage` needs careful origin validation.

Always weigh the benefits against these potential drawbacks.

Custom Communication Check

You're implementing a Micro Frontend architecture. One MFE is embedded in an iframe on a different domain. You need to send simple messages between the host and the iframe securely.

Recap: Custom Solutions

We explored custom communication solutions for Micro Frontends, going beyond event buses and shared state.

Direct Callbacks: For tightly coupled components.
postMessage API: For secure cross-origin communication, especially with iframes.
Shared Registries: For lightweight, custom global data/services.

Remember to carefully consider the trade-offs of increased coupling and complexity before opting for a custom approach.

Frequently asked questions

Is the “Custom Communication Solutions” lesson free?

Yes — the full text of “Custom Communication Solutions” is free to read here on the web, and the Micro Frontends Architecture with Module Federation course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Micro Frontends Architecture with Module Federation course, upgrade to CoddyKit PRO.

What will I learn in “Custom Communication Solutions”?

Design and implement custom communication mechanisms tailored to specific Micro Frontend needs. You practise Micro Frontends Architecture with Module Federation with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Micro Frontends Architecture with Module Federation?

No prior experience is required. Micro Frontends Architecture with Module Federation on CoddyKit is structured for beginners through advanced learners; this is — lesson 3 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Custom Communication Solutions” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Micro Frontends Architecture with Module Federation lesson?

Yes. Every Micro Frontends Architecture with Module Federation lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

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