Shared Configuration

Shared Configuration Overview

At its core, shared configuration is about doing one thing well inside your single-spa project. Once you understand the pattern, you can apply it consistently across features and teams.

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

// shared utility module exposed via the import map
export const authService = {
  getToken: () => localStorage.getItem('token'),
};

// consumed by any micro frontend
import { authService } from '@org/utils';

Shared utility modules provide cross-app services like auth without tight coupling.

Shared Configuration Example

registerApplication({
  name: '@org/app',
  app: () => System.import('@org/app'),
  activeWhen: ['/app'],
});
start();

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

Single-SPA Cheatsheet

Core single-spa APIs related to shared configuration.

How Shared Configuration Works in Single-SPA

Shared Configuration is part of how single-spa lets multiple applications — even in different frameworks — coexist on one page. A root config registers each app and controls when it is active.

Shared utility modules provide cross-app services like auth without tight coupling.

• A root config registers apps and calls start().
• Each app exports bootstrap, mount, and unmount lifecycles.
• activeWhen decides which routes each app owns.
• Import maps resolve each app's bundle at runtime.

Practical Guidance for Shared Configuration

For reliable micro frontends, shared configuration should isolate failures and keep shared state minimal. Let each team own its app end to end while agreeing on a few shared contracts.

Common Mistakes

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

Key Takeaways

• Shared Configuration is a core part of working effectively with single-spa.
• Start small and keep shared configuration focused on a single responsibility.
• Apply consistent patterns so shared configuration scales across your project.
• Test and document shared configuration to keep it maintainable over time.