Single-SPA Debugging

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

Debugging Overview

Debugging 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 debugging 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.

Debugging Example

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

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

Single-SPA Cheatsheet

Core single-spa APIs related to debugging.

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 Debugging Works in Single-SPA

Debugging 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 Debugging

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

Key Takeaways

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

Pro Tip

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