new HTMLParser(content).body.getElementByXPath("/a...").href

$(await fetch('url')).find('a').setAttr('href', 'Hi')

javascript
class LinkHandler {
  element(element) {
    element.setAttribute('href', 'https://gregbrimble.com/')
  }
}

addEventListener('fetch', event => {
  event.respondWith(handleRequest(event.request))
})

/**
 * Fetch and log a given request object
 * @param {Request} request
 */
async function handleRequest(request) {
  console.log('Got request', request)
  const response = await fetch(request)
  return new HTMLRewriter().on('a', new LinkHandler()).transform(response)
}