Mixed-Framework Routing

Mixed-Framework Routing is an important part of building production-ready single-spa systems. This lesson explains what mixed-framework routing means, how it works, and how to apply it with practical examples you can reuse.

Mixed-Framework Routing Overview

Mixed-Framework Routing 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 mixed-framework routing 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.

registerApplication({
  name: '@org/checkout',
  app: () => System.import('@org/checkout'),
  activeWhen: (location) => location.pathname.startsWith('/checkout'),
});

activeWhen decides which route ranges a micro frontend owns.

Mixed-Framework Routing Example

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

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

Single-SPA Cheatsheet

Core single-spa APIs related to mixed-framework routing.

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 Mixed-Framework Routing Works in Single-SPA

Mixed-Framework Routing 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.

activeWhen decides which route ranges a micro frontend owns.

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 Mixed-Framework Routing

For reliable micro frontends, mixed-framework routing 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

Copying mixed-framework routing snippets without understanding what each line does.
Skipping error handling and edge cases when wiring up mixed-framework routing.
Leaving mixed-framework routing untested, so regressions slip into production.
Over-engineering mixed-framework routing before you actually need the extra flexibility.

Key Takeaways

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

Pro Tip

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