Import Map Configuration

Import Map Configuration is an important part of building production-ready single-spa systems. This lesson explains what import map configuration means, how it works, and how to apply it with practical examples you can reuse.

Import Map Configuration Overview

Import Map Configuration lets you structure single-spa work so it stays readable, testable, and easy to scale. Instead of ad-hoc code, you follow a clear pattern that other developers can recognise immediately.

The key is to keep import map configuration focused and predictable. Start from the minimal example here, then layer in only the complexity your feature actually needs.

<script type="systemjs-importmap">
{
  "imports": {
    "@org/root-config": "//localhost:9000/org-root-config.js",
    "@org/navbar": "//localhost:8500/org-navbar.js"
  }
}
</script>

Import maps tell SystemJS where to load each micro frontend bundle at runtime.

Import Map Configuration Example

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

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

Single-SPA Cheatsheet

Core single-spa APIs related to import map configuration.

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 Import Map Configuration Works in Single-SPA

Import Map Configuration 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.

Import maps tell SystemJS where to load each micro frontend bundle at runtime.

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 Import Map Configuration

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

Key Takeaways

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

Pro Tip

When you get stuck on import map configuration, reduce it to the smallest reproducible example first — most single-spa issues become obvious once the noise is gone.