docs/javascripts/release-notes.js

export default function releaseNotes () {
  const patches = Array.from(document.querySelectorAll('.js-release-notes-patch'))
  if (patches.length === 0) return

  const observer = new IntersectionObserver((entries) => {
    for (const entry of entries) {
      const { version } = entry.target.dataset
      const patchLink = document.querySelector(`.js-release-notes-patch-link[data-version="${version}"]`)
      patchLink.classList.toggle('selected', entry.isIntersecting)
    }
  }, {
    rootMargin: '-40% 0px -50%'
  })

  patches.forEach(patch => {
    observer.observe(patch)
  })
}