Application Shell

Application Shell Overview

At its core, application shell 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 shell 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 Shell Example

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

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

Single-SPA Cheatsheet

Core single-spa APIs related to application shell.

How Application Shell Works in Single-SPA

Application Shell 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 Shell

For reliable micro frontends, application shell should isolate failures and keep shared state minimal. Let each team own its app end to end while agreeing on a few shared contracts.

Common Mistakes

• Skipping error handling and edge cases when wiring up application shell.
• Leaving application shell untested, so regressions slip into production.
• Over-engineering application shell before you actually need the extra flexibility.
• Ignoring documentation, which makes application shell hard for the next developer to change.

Key Takeaways

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