Single-SPA Resources

Resources sits at the heart of reference in single-spa. This guide walks through the concept step by step, with examples, a cheatsheet, and common mistakes to avoid.

Resources Overview

Resources 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 resources 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.

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.

Resources Example

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

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

Single-SPA Cheatsheet

Core single-spa APIs related to resources.

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 Resources Works in Single-SPA

Resources 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 Resources

For reliable micro frontends, resources 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 resources.
Leaving resources untested, so regressions slip into production.
Over-engineering resources before you actually need the extra flexibility.
Ignoring documentation, which makes resources hard for the next developer to change.

Key Takeaways

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

Pro Tip

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