Switching the baseUrl in Eleventy.js

deploy.yml

name: Build and Deploy
on:
  push:
    branches: [ master ]
jobs:
  build-and-deploy:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout 🛎️
        uses: actions/checkout@v2
        with:
          persist-credentials: false

      - name: Install and Build 🔧
        run: |
          npm ci
          npm test
          npm run build -- --pathprefix=/repository-name/
        env:
          GITHUB_URL: https://username.github.io

      - name: Deploy 🚀
        uses: JamesIves/github-pages-deploy-action@releases/v3
        with:
          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
          BRANCH: gh-pages
          FOLDER: dist

site.js

const site = {
  baseUrl: '/',
}

module.exports = () => {
  if (process.env.ELEVENTY_BASE_URL) {
    site.baseUrl = process.env.ELEVENTY_BASE_URL
  }

  // https://docs.netlify.com/configure-builds/environment-variables/#deploy-urls-and-metadata
  if (process.env.URL) {
    site.baseUrl = process.env.URL
  }

  // https://vercel.com/docs/v2/build-step#system-environment-variables
  if (process.env.VERCEL_URL) {
    site.baseUrl = process.env.VERCEL_URL
  }

  // https://help.github.com/en/actions/configuring-and-managing-workflows/using-environment-variables
  if (process.env.GITHUB_URL) {
    site.baseUrl = process.env.GITHUB_URL
  }

  return site
}