Cross-Framework Integration

Understanding cross-framework integration helps you work with single-spa confidently. Here you will learn the core ideas behind cross-framework integration, see working code, and pick up best practices used on real teams.

Cross-Framework Integration Overview

Cross-Framework Integration is a building block you will reach for often in single-spa. It keeps related logic together and makes your intent obvious to reviewers and future maintainers.

When you learn cross-framework integration properly, you avoid the guesswork that leads to bugs and rework. The example below shows the shape you will use in most real single-spa projects.

// 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.

Cross-Framework Integration Example

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

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

Single-SPA Cheatsheet

Core single-spa APIs related to cross-framework integration.

API	Example	Purpose
registerApplication	`registerApplication({ name, app, activeWhen })`	Register a micro frontend
activeWhen	`activeWhen: ['/checkout']`	Route ownership
start	`start()`	Begin routing
bootstrap	`export async function bootstrap()`	One-time setup
mount	`export async function mount(props)`	Render the app
unmount	`export async function unmount(props)`	Clean up the app
import map	`systemjs-importmap`	Locate app bundles

How Cross-Framework Integration Works in Single-SPA

Cross-Framework Integration 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 Cross-Framework Integration

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

Concern	Recommendation
Isolation	One app's crash should not break others
Shared state	Prefer shared utility modules over globals
Routing	Keep activeWhen rules explicit and non-overlapping
Deployment	Release via import-map updates per app

Common Mistakes

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

Key Takeaways

Cross-Framework Integration is a core part of working effectively with single-spa.
Start small and keep cross-framework integration focused on a single responsibility.
Apply consistent patterns so cross-framework integration scales across your project.
Test and document cross-framework integration to keep it maintainable over time.

Pro Tip

Pair cross-framework integration with automated tests from day one. It is far cheaper to catch single-spa regressions in CI than in production.