Custom Events

Custom Events Overview

At its core, custom events 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 custom events 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.

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

Module Federation Cheatsheet

Key Module Federation settings related to custom events.

How Custom Events Works in Module Federation

Custom Events 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 Custom Events

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

Key Takeaways

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