Style Isolation

Style Isolation Overview

At its core, style isolation is about doing one thing well inside your Module Federation project. Once you understand the pattern, you can apply it consistently across features and teams.

Good style isolation pays off across the whole codebase: fewer surprises, easier testing, and smoother onboarding. The snippet below is a solid starting point.

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.

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

Module Federation Cheatsheet

Key Module Federation settings related to style isolation.

How Style Isolation Works in Module Federation

Style 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 Style Isolation

In production, style 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

• Skipping error handling and edge cases when wiring up style isolation.
• Leaving style isolation untested, so regressions slip into production.
• Over-engineering style isolation before you actually need the extra flexibility.
• Ignoring documentation, which makes style isolation hard for the next developer to change.

Key Takeaways

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