Component Versioning

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

Component Versioning Overview

Component Versioning 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 component versioning 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.

# each micro frontend publishes its own bundle + import-map entry
@org/checkout -> https://cdn.example.com/checkout/v3/checkout.js

# update only this app's import-map entry to release it
{ "@org/checkout": "https://cdn.example.com/checkout/v3/checkout.js" }

Deploying a micro frontend is often just updating its import-map URL.

Component Versioning Example

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

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

Single-SPA Cheatsheet

Core single-spa APIs related to component versioning.

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 Component Versioning Works in Single-SPA

Component Versioning 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.

Deploying a micro frontend is often just updating its import-map URL.

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 Component Versioning

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

Key Takeaways

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

Pro Tip

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