Shared State

Shared State Overview

Shared State is a building block you will reach for often in Module Federation. It keeps related logic together and makes your intent obvious to reviewers and future maintainers.

When you learn shared state properly, you avoid the guesswork that leads to bugs and rework. The example below shows the shape you will use in most real Module Federation projects.

new ModuleFederationPlugin({
  name: 'shell',
  shared: {
    react: { singleton: true, requiredVersion: '^18.2.0' },
    'react-dom': { singleton: true, requiredVersion: '^18.2.0' },
  },
});

Marking shared libraries as singletons ensures one React instance is used across all micro frontends.

Shared State Example

new ModuleFederationPlugin({
  name: 'app',
  filename: 'remoteEntry.js',
  exposes: { './Widget': './src/Widget' },
  remotes: { other: 'other@http://host/remoteEntry.js' },
  shared: { react: { singleton: true } },
});

• Start from a minimal Shared State example and grow it only as needed.
• Keep configuration explicit so Shared State behaves the same in every environment.
• Name things clearly so teammates understand your Shared State at a glance.
• Add tests around Shared State early to lock in expected behaviour.

Module Federation Cheatsheet

Key Module Federation settings related to shared state.

How Shared State Works in Module Federation

Shared State builds on Module Federation's ability to load code from another independently built and deployed application at runtime. Each app can be a host, a remote, or both.

Marking shared libraries as singletons ensures one React instance is used across all micro frontends.

• Remotes expose modules through a remoteEntry.js manifest.
• Hosts declare remotes and import exposed modules dynamically.
• Shared dependencies are deduplicated, ideally as singletons.
• Each micro frontend builds and deploys on its own schedule.

Practical Guidance for Shared State

In production, shared state needs careful version management and graceful failure handling. Align shared dependency versions and always render a fallback when a remote cannot load.

Common Mistakes

• Copying shared state snippets without understanding what each line does.
• Skipping error handling and edge cases when wiring up shared state.
• Leaving shared state untested, so regressions slip into production.
• Over-engineering shared state before you actually need the extra flexibility.

Key Takeaways

• Shared State is a core part of working effectively with Module Federation.
• Start small and keep shared state focused on a single responsibility.
• Apply consistent patterns so shared state scales across your project.
• Test and document shared state to keep it maintainable over time.