As applications grow in size and complexity, managing a monolithic front-end codebase can become cumbersome. One solution is adopting Micro Frontends, a technique that allows teams to break up a large front-end into smaller, independent applications that work together seamlessly. In this post, we’ll explore the why behind Micro Frontends and discuss how to implement them effectively in a React.js environment. As always, let’s start from the beginning.

What are Micro Frontends?

Micro Frontends apply the concepts of microservices to the front-end world. Each feature or module in a large-scale application can be thought of as an independent application (or “micro app”), responsible for its own state and rendering logic. These micro apps are then stitched together to form a cohesive user experience.

• Separation of Concerns: Each team can work on a specific feature or section of the UI without impacting the rest of the application.
• Independent Deployments: Micro Frontends enable independent deployments. Teams can deploy changes to one micro app without redeploying the entire front-end.

Why use Micro Frontends?

Some of the benefits of using Micro Frontends in large React.js applications include:

• Scalability: Micro Frontends allow multiple teams to work on different parts of the UI simultaneously, speeding up development time and reducing bottlenecks.
• Technology Agnostic: Each micro app can be built using different technologies, allowing for experimentation or gradual migration to new technologies.
• Code Ownership: Teams own their micro frontends, meaning they have full responsibility for development, testing, and deployment, which promotes accountability.

How to Implement Micro Frontends in React.js?

There are several architectural approaches for implementing them:

• Iframe-based Isolation: This is the most basic approach, where each micro frontend is rendered inside an iframe. This provides true isolation but lacks seamless user experience and introduces communication challenges.

• Module Federation (Webpack 5): Webpack 5 introduced Module Federation, which enables different React apps (micro apps) to share code and dependencies while still being independently deployed. This approach allows seamless integration of multiple Micro Frontends without the isolation issues of iframes. For example:

// Example: Dynamically loading micro frontends using Webpack 5's module federation
import { Suspense, lazy } from "react";
const MicroFrontend = lazy(() => import("remoteApp/MicroApp"));

const App = () => (
  <Suspense fallback={<div>Loading...</div>}>
    <MicroFrontend />
  </Suspense>
);

• Single-SPA Framework: Single-SPA is an open-source framework designed for Micro Frontends. It lets you build and orchestrate multiple Micro Frontends on a single page, managing routing and lifecycle events across them:

import { registerApplication, start } from 'single-spa';

registerApplication({
  name: "@organization/navbar",
  app: () => import("@organization/navbar"),
  activeWhen: ["/"],
});

start();

How Micro Frontends communicate between them

Micro Frontends should be as isolated as possible, but communication is inevitable. Popular methods include:

• Global Event Bus: Create an event system that allows micro apps to communicate without tightly coupling them.
• Custom API Contracts: Expose specific APIs between micro frontends to share data safely and efficiently.

Challenges

Despite the advantages, there are challenges to be aware of:

• Performance Overhead: Each micro app might load its own set of dependencies, leading to potential performance hits.
• Shared State: Managing global state between micro apps can be tricky. Using a shared service or library can help, but it requires careful design.

Conclusion

Micro Frontends offer a powerful way to scale React.js applications, especially when multiple teams are involved. While there are trade-offs, this architectural style enables independent development, streamlined deployments, and more maintainable front-end codebases.