Logs all new chat messages into the browser console. Uses the MutationObserver API

TwitchLogger.js

(function () {
  // Sources from https://stackoverflow.com/a/14570614/12697448
  // Thanks vsync for the spectacular code
  var observeDOM = (function () {
    var MutationObserver = window.MutationObserver || window.WebKitMutationObserver;

    return function (obj, callback) {
      if (!obj || !obj.nodeType === 1)
        return; // validation

      if (MutationObserver) {
        // define a new observer
        var obs = new MutationObserver(function (mutations, observer) {
            callback(mutations);
          })
          // have the observer observe foo for changes in children
          obs.observe(obj, {
            childList: true,
            subtree: true
          });
      } else if (window.addEventListener) {
        obj.addEventListener('DOMNodeInserted', callback, false);
        obj.addEventListener('DOMNodeRemoved', callback, false);
      }
    }
  })();

  const chatListContainers = document.getElementsByClassName('chat-list__list-container');

  if (chatListContainers.length === 0) {
    console.error('Unable to find the chat list container element.');

    return;
  }

  // Get the first one
  const selectedChatList = chatListContainers[0];

  // Use the MutationObserver to track changes on the chat element
  observeDOM(selectedChatList, function (emmy) {
    // Loop through all elements which have been modified
    for (let i = 0; i < emmy.length; i++) {
      // Added chat elements/nodes
      const addedNodes = emmy[i].addedNodes;

      // If there are added nodes continue
      if (addedNodes.length > 0) {

        // Loop through each node
        for (let nodeCount = 0; nodeCount < addedNodes.length; nodeCount++) {
          // Log the text of the node (non-formatted)
          console.log(addedNodes[nodeCount].innerText);
        }
      }
    }
  });

})();