Single-Spa with Angular v17+ and native ESM

What is this?

This is an example Nx monorepo demonstrating how single-spa can be used for microfrontends with the new Angular builder based on Vite/esbuild.

Goals:

• Angular micro-frontend apps, served/bundled as native ES Modules by Vite/esbuild
• Leverage native browser importmap support
• Support for having multiple importmaps (thanks to import-map-injector)
• Support for external importmaps (thanks to import-map-injector)
• Support for overriding importmaps (thanks to import-map-overrides)
• Route-based loading of micro-frontends (handled by single-spa)
• Live-reload functionality during development
• Share dependencies between Angular micro-frontends

Want to learn more?

I've written some more in-depth background in a seprate markdown doc. I encourage you to read it if you are interested to learn more about the reasoning behind all of this: background.md

Try it out

To get started, first we need to install our dependencies:

pnpm i

NOTE: pnpm has a nice patch feature, which I use sometimes to unblock Nx or Angular upgrades: https://pnpm.io/cli/patch.

To run the application, we need to start the dev-server on each of the apps in the repo:

• the app-shell (the root html file with importmaps etc)
• the host module (MF orchestration logic, or in simple terms: some vanilla JS that calls singleSpa.registerApplication())
• the navbar MF
• the 2 main MF apps (cats and dogs)

To do this, we could open 5 separate terminal windows and run the serve target for each of these apps separately (e.g. pnpm nx serve app-shell etc).

OR, to make it easier, we can run the dev script which leverages Nx to start them all at once in parallel:

pnpm dev

Give it a few seconds until all the dev servers are up-and-running. Then we are ready to see it in action by opening the app-shell url in our browser: http://localhost:4300/

Override the importmap

One feature that makes this architecture really shine, is the ability to override specific modules in the importmap, for local development. To enable this, we used the import-map-overrides library (we load this script from our app-shell page).

To try it out, you can follow these steps:

Step 1. Serve 1 micro-frontend app locally. For example:

pnpm nx serve cats

Step 2. Visit deployed application in your browser: https://single-spa-angular-esm.vercel.app/

Step 3. Open the JS console and execute the following javascript command

localStorage.setItem('overrides-ui', true)

Step 4. Refresh the page in the browser.

Step 5. Now you should see a yellow-ish rounded square button near the bottom-right corner of the page. Click it, and override the module named @myorg/cats with the URL of the locally served micro-frontend app: http://localhost:4201/main.js

Step 6. Refresh the page once more. Now you are set up to start making local changes to the cats app and see these changes reflected in the browser immediately 🎉🚀