Application Status

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

Application Status Overview

At its core, application status 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 application status 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/app',
  app: () => System.import('@org/app'),
  activeWhen: ['/app'],
});

start();

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

Application Status Example

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

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

Single-SPA Cheatsheet

Core single-spa APIs related to application status.

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 Application Status Works in Single-SPA

Application Status 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 Application Status

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

Key Takeaways

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

Pro Tip

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