Root Configuration

In this lesson you will learn root configuration in single-spa, why it matters within core concepts, and how to use it correctly with clear, copy-ready examples.

Root Configuration Overview

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

import { registerApplication, start } from 'single-spa';

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

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

start();

The root config registers each micro frontend and starts single-spa's routing.

Root Configuration Example

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

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

Single-SPA Cheatsheet

Core single-spa APIs related to root configuration.

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 Root Configuration Works in Single-SPA

Root 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.

The root config registers each micro frontend and starts single-spa's routing.

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 Root Configuration

For reliable micro frontends, root 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.

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

Key Takeaways

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

Pro Tip

Bookmark this root configuration pattern and reuse it. Consistency across your single-spa codebase is worth more than clever one-off solutions.