componentWillUnmount/beforeDestroy in alpine.js

example.html

<div x-data @remove='console.log($el, "removed")'></div>

remove.js

const observer = new MutationObserver(mutations => {
  for (const mutation of mutations) {
    if (mutation.type !== 'childList') continue

    mutation.removedNodes.forEach(node => {
      if (node.nodeType !== Node.ELEMENT_NODE) return

      [node, ...node.querySelectorAll('[\\@remove]')].forEach(node => {
        node.dispatchEvent(new CustomEvent('remove'))
      })
    })
  }
})

observer.observe(document, {
  childList: true,
  subtree: true
})