Dynamic Import Maps

Dynamic Import Maps Overview

At its core, dynamic import maps 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 dynamic import maps 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.

Dynamic Import Maps Example

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

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

Single-SPA Cheatsheet

Core single-spa APIs related to dynamic import maps.

How Dynamic Import Maps Works in Single-SPA

Dynamic Import Maps 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 Dynamic Import Maps

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

Key Takeaways

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