scrollUpMessenger.js

// Hey there, I made a simple script to scroll up Messenger chats.

/* How to use: 
  1. On the desktop Messenger client, run the following code in the DevTools console.
  2. start() // starts scrolling up the main chat window
  3. stop() // stops scrolling
*/

let on = null;

const start = () => {
  if (!on) {
    scrollUp();
    return "Scrolling up and up!!";
  }
};

const stop = () => {
  if (on) {
    clearInterval(on);
    on = null;
    return "Scrolling stopped.";
  }
};

// scrollUp() selects the middle chat window and scrolls up every 500 milliseconds
function scrollUp() {
  on = setInterval(function () {
    document
      .querySelector("iframe")
      .contentWindow.document.querySelectorAll(".scrollable")[2].scrollTop = 0;
  }, 500);
}