With this we now have a single-spa root config and an application, but they are in the same repository and when bundled we only get our normal vite output:

> tsc && vite build

vite v4.4.9 building for production...
✓ 38 modules transformed.
dist/index.html                   0.49 kB │ gzip:  0.32 kB
dist/assets/react-35ef61ed.svg    4.13 kB │ gzip:  2.14 kB
dist/assets/main-d526a0c5.css     1.42 kB │ gzip:  0.74 kB
dist/assets/index-56826ec8.js    21.63 kB │ gzip:  7.35 kB
dist/assets/main-4bcda428.js    143.07 kB │ gzip: 45.96 kB
✓ built in 880ms

Even if we host our application somewhere the hash for our main.js will change every time we make any changes. Any outside root config application will lose track of our application with this.

Vite also assumes that any assets and split js chunks will be found with a base url of / which isn't true if our app is called from a different domain.

In vite we can set the base url via the base config option. In order to keep this flexible for each environment we will want to read this from a config option

import { defineConfig, loadEnv } from 'vite'
import react from '@vitejs/plugin-react'

// https://vitejs.dev/config/
export default defineConfig(({ mode }) => {
  const env = loadEnv(mode, '', 'VITE_');
  return {
    plugins: [react()],
    base: env.VITE_BASE_URL
  };
})

.env.development

VITE_BASE_URL=/

{
  "build": {
    "rollupOptions": {
      "input": {
        "root-config": "src/root-config.ts",
        "main": "src/main.tsx"
      },
      "output": {
        "entryFileNames": "[name].js",
        "format": "system"
      }
    }
  }
}

With this the format of systemjs should make it consumable from the outside and the input and output options should ensure that we have stable outputs

> tsc && vite build

vite v4.4.9 building for production...
✓ 37 modules transformed.
dist/assets/react-35ef61ed.svg    4.13 kB │ gzip:  2.14 kB
dist/assets/main-20fab710.js      1.27 kB │ gzip:  0.66 kB
dist/root-config.js              20.18 kB │ gzip:  6.71 kB
dist/main.js                    143.56 kB │ gzip: 46.27 kB
✓ built in 924ms