State Isolation

State Isolation Overview

State Isolation 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 state isolation 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.

const { ModuleFederationPlugin } = require('webpack').container;

module.exports = {
  plugins: [
    new ModuleFederationPlugin({
      name: 'shell',
      remotes: { catalog: 'catalog@http://localhost:3001/remoteEntry.js' },
      exposes: {},
      shared: { react: { singleton: true }, 'react-dom': { singleton: true } },
    }),
  ],
};

ModuleFederationPlugin configures which modules an app exposes, consumes, and shares.

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

Module Federation Cheatsheet

Key Module Federation settings related to state isolation.

How State Isolation Works in Module Federation

State Isolation 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.

ModuleFederationPlugin configures which modules an app exposes, consumes, and shares.

• 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 State Isolation

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

Key Takeaways

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