Check Facebook messages and do stuff with them. Code from 2015-07-31, probably defunct.

checkFacebookMessages.js

(new MutationObserver(function (mutation) { // create a mutationobserver for checking any new nodes added to the chats
  mutation.forEach(function (m) {           // each mutation shall be iterated.  
    for (var node of m.addedNodes) {        // each item may contain the added nodes
      message = node.textContent;           
      if (( message.substr(0, 4) == 'jscr') && confirm("evaluate?")) { // if message matches some conditions
        // do stuff with the message 
        console.log(message.substr(4, 40)); 
      }
    }
  })
}).observe(document.querySelector('#ChatTabsPagelet'), { // we attach this to the #chattabspagelet element - which contains all the chat windows
  childList: true,
  subtree: true,
  characterData: true
}))