Path-Based Routing

In this lesson you will learn path-based routing in single-spa, why it matters within routing, and how to use it correctly with clear, copy-ready examples.

Path-Based Routing Overview

Path-Based 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 path-based 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.

Path-Based Routing Example

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

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

Single-SPA Cheatsheet

Core single-spa APIs related to path-based 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 Path-Based Routing Works in Single-SPA

Path-Based 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 Path-Based Routing

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

Key Takeaways

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

Pro Tip

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