Eager Loading

Eager Loading Overview

Eager Loading 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 eager loading 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.

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

Module Federation Cheatsheet

Key Module Federation settings related to eager loading.

How Eager Loading Works in Module Federation

Eager Loading 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 Eager Loading

In production, eager loading 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 eager loading.
• Leaving eager loading untested, so regressions slip into production.
• Over-engineering eager loading before you actually need the extra flexibility.
• Ignoring documentation, which makes eager loading hard for the next developer to change.

Key Takeaways

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