Team Contracts

Team Contracts is an important part of building production-ready single-spa systems. This lesson explains what team contracts means, how it works, and how to apply it with practical examples you can reuse.

Team Contracts Overview

Team Contracts lets you structure single-spa work so it stays readable, testable, and easy to scale. Instead of ad-hoc code, you follow a clear pattern that other developers can recognise immediately.

The key is to keep team contracts focused and predictable. Start from the minimal example here, then layer in only the complexity your feature actually needs.

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

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

start();

single-spa orchestrates multiple framework apps on one page through a root config.

Team Contracts Example

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

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

Single-SPA Cheatsheet

Core single-spa APIs related to team contracts.

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 Team Contracts Works in Single-SPA

Team Contracts 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.

single-spa orchestrates multiple framework apps on one page through a root config.

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 Team Contracts

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

Key Takeaways

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

Pro Tip

When you get stuck on team contracts, reduce it to the smallest reproducible example first — most single-spa issues become obvious once the noise is gone.