Chrome extensions CORB: How to react to updates in the shared DOM

Question

Trying to build a chrome extension content script that adds an extra useful nav to a GitHub issue page. When interaction is done through the normal webpage (the end user click an reaction emoji) - my injected element gets lost.

The only way I have been able to get around it is to set an interval that keeps removing and injecting my counter element into the page.

There must be a more elegant way than this that allows a responsive reaction to DOM changes so I can then remove and re-inject the element (instead of banging on the door all the time)?

The extension I'm trying to optimize can be found here

https://github.com/NorfeldtAbtion/github-issue-reactions-chrome-extension

The important files currently looks like this

addReactionsNav.js

const URL =
  window.location.origin + window.location.pathname + window.location.search
const header = document.querySelector('#partial-discussion-sidebar')
header.style = `position: relative;height: 100%;`
let wrapper = getWrapper()

// // The isolated world made it difficult to detect DOM changes in the shared DOM
// // So this monkey-hack to make it refresh when ..
// setInterval(() => {
//   wrapper.remove()
//   wrapper = getWrapper()
//   addReactionNav()
// }, 1000)

// Select the node that will be observed for mutations
const targetNode = document.querySelector('body')

// Options for the observer (which mutations to observe)
const config = { attributes: true, childList: true, subtree: true }

// Create an observer instance linked to the callback function
const observer = new MutationObserver(() => addReactionNav())

// Start observing the target node for configured mutations
observer.observe(targetNode, config)

function getWrapper() {
  const header = document.querySelector('#partial-discussion-sidebar')
  const wrapper = header.appendChild(document.createElement('div'))
  wrapper.style = `
      position:sticky;
      position: -webkit-sticky;
      top:10px;`
  return wrapper
}

function addReactionNav() {
  const title = document.createElement('div')
  title.style = `font-weight: bold`
  title.appendChild(document.createTextNode('Reactions'))
  wrapper.appendChild(title)

  // Grabbing all reactions Reactions �� �� �� �� ❤️ �� �� ��
  const reactionsNodes = document.querySelectorAll(`
    [alias="+1"].mr-1,
    [alias="rocket"].mr-1,
    [alias="tada"].mr-1,
    [alias="heart"].mr-1,
    [alias="smile"].mr-1,
    [alias="thinking_face"].mr-1,
    [alias="-1"].mr-1,
    [alias="eyes"].mr-1
  `)

  const reactionsNodesParents = [
    ...new Set(
      Array.from(reactionsNodes).map(node => node.parentElement.parentElement)
    ),
  ]

  reactionsNodesParents.forEach(node => {
    const a = document.createElement('a')
    const linkText = document.createTextNode('\n' + node.innerText)
    a.appendChild(linkText)
    a.title = node.innerText

    let id = null
    while (id == null || node != null) {
      if (node.tagName === 'A' && node.name) {
        id = node.name
        break
      }

      if (node.id) {
        id = node.id
        break
      }

      node = node.parentNode
    }
    const postURL = URL + '#' + id
    a.href = postURL
    a.style = `display:block;`

    wrapper.appendChild(a)
  })
}

manifest.json

{
  "manifest_version": 2,
  "name": "Github Issue Reactions",
  "version": "1.0",
  "description": "List a link of reactions on a github issue page",
  "permissions": ["https://www.github.com/", "http://www.github.com/"],
  "content_scripts": [
    {
      "matches": ["*://*.github.com/*/issues/*"],
      "js": ["addReactionsNav.js"],
      "run_at": "document_end"
    }
  ]
}

---

Found this brief mention about "isolated worlds"

https://youtu.be/laLudeUmXHM?t=79

Update

I now believe that the "bug" is due to CORB - which is a security measure against Spectre.

Cross-Origin Read Blocking (CORB) blocked cross-origin response https://api.github.com/_private/browser/stats with MIME type application/json. See https://www.chromestatus.com/feature/5629709824032768 for more details.

Google explain more about it in their talk Lessons from Spectre and Meltdown, and how the whole web is getting safer (Google I/O '18)

The example mentioned at 34:00 seems to have been blocked by CORB since.

Answer 1

As GitHub replaces the whole #partial-discussion-sidebar node when "the end-user clicks a reaction emoji" on the first post, you need to getWrapper() again before addReactionNav() in your mutation observer response, as is shown below.

Update: As the #partial-discussion-sidebar node is not rerendered in case of reactions updating on posts other than the first one, we also need to respond to the timeline items' update.

const URL = window.location.origin + window.location.pathname + window.location.search;
const header = document.querySelector('#partial-discussion-sidebar');
header.style = `position: relative;height: 100%;`;
let wrapper = getWrapper();
addReactionNav();    // Initial display.

// Select the node that will be observed for mutations.
const targetNode = document.querySelector('body');

// Options for the observer (which mutations to observe).
const config = {
  childList: true,
  subtree: true
};

// Create an observer instance linked to the callback function.
const observer = new MutationObserver(mutations => {
  if (!targetNode.contains(wrapper) || mutations.some(mutation => mutation.target.matches('.js-timeline-item'))) {
    wrapper.remove();
    wrapper = getWrapper();
    addReactionNav();
  }
});

// Start observing the target node for configured mutations.
observer.observe(targetNode, config);