Fallback Components

Fallback Components Overview

Fallback Components 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 fallback components 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 ProductList = React.lazy(() =>
  import('catalog/ProductList').catch(() => ({
    default: () => <p>Catalog is temporarily unavailable</p>,
  })),
);

Always provide a fallback so a failing remote degrades gracefully instead of crashing the shell.

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

Module Federation Cheatsheet

Key Module Federation settings related to fallback components.

How Fallback Components Works in Module Federation

Fallback Components 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.

Always provide a fallback so a failing remote degrades gracefully instead of crashing the shell.

• 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 Fallback Components

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

Key Takeaways

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