javascript: (function () {

const log = function (msg) {
  const d = new Date();
  const n = d.toISOString();
  console.log(`${n} - ${msg}`);
};

const clickMenu = function() {
  document
    .querySelector('[aria-label="Conversation actions"]')
    .click();
  log('Opening the dropdown menu');
};

const clickDeleteFromMenu = function () {
  document
    .getElementsByClassName('uiContextualLayer')[0]
    .getElementsByTagName('ul')[0]
    .getElementsByClassName('__MenuItem')[3]
    .click();
  log('Clicking Delete');
};

const clickDeleteButton = function () {
  document
    .querySelector('[aria-label="Dialog content"]')
    .getElementsByTagName('button')[1]
    .click();
  log('Confirming Delete');
};

const deleteFacebookMessages = function() {
  setTimeout(clickMenu, 500);
  setTimeout(clickDeleteFromMenu, 800);
  setTimeout(clickDeleteButton, 1000);
};

const messageExist = function () {
  return document.querySelector('[aria-label="Conversation List"] li [role="gridcell"]');
};

const run = function () {
  if ( messageExist !== null || messageExist !== undefined ){
    deleteFacebookMessages();
  }
};

run();

})();