Local Import Map Overrides

Local Import Map Overrides Overview

At its core, local import map overrides 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 local import map overrides pays off across the whole codebase: fewer surprises, easier testing, and smoother onboarding. The snippet below is a solid starting point.

<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.

Local Import Map Overrides Example

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

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

Single-SPA Cheatsheet

Core single-spa APIs related to local import map overrides.

How Local Import Map Overrides Works in Single-SPA

Local Import Map Overrides 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 Local Import Map Overrides

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

Key Takeaways

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