Single-SPA Performance

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

Performance Overview

Performance 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 performance 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.

Performance Example

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

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

Single-SPA Cheatsheet

Core single-spa APIs related to performance.

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 Performance Works in Single-SPA

Performance 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 Performance

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

Key Takeaways

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

Pro Tip

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