Batch Messages on WhatsApp Web

batch-messages.user.js

// ==UserScript==
// @name        Batch Messages on WhatsApp Web
// @namespace   [email protected]
// @include     https://web.whatsapp.com/
// @version     1
// @grant       unsafeWindow
// ==/UserScript==

// !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! //
// Disclaimer: WhatsApp is banning people who use this //
// !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! //

checkButton();

function checkButton(){
  var menuButton = document.querySelector('button.icon-menu[data-reactid*="$conversation-header"]');
  if (menuButton) {
    menuButton.onclick = addAction;
  } else {
    setTimeout(checkButton, 1000);
  }
}

function addAction (){
  var headerMenuList = document.querySelector('ul[data-reactid*="$conversation-header"]');
  if (!headerMenuList) { return setTimeout(addAction, 150); }
  var newListElement = document.createElement('li');
  newListElement.className = 'menu-item menu-shortcut';
  newListElement.style.opacity = 1;
  var newListAnchor = document.createElement('a');
  newListAnchor.onclick = createSendScript;
  newListAnchor.textContent = 'Send last message to all contacts';
  newListElement.appendChild(newListAnchor);
  headerMenuList.appendChild(newListElement);
  
  (function check(){
    if (newListElement.parentNode) {
      setTimeout(check, 1000);
    } else {
      checkButton();
    }
  }());
}

function createSendScript() {
  unsafeWindow.eval('('+sendMessages+'());');
}

function sendMessages() {
  var b = Store.Chat.models.filter(function(a) {
    return a.active;
  })[0].msgs.last().attributes.body;
  
  if(confirm('You\'re sure that you want to send this message\n"' + b + '"\nto everyone?')) {
    Store.Chat.models.filter(function(a) {
      return !a.active;
    }).forEach(function(a) {
      a.sendMessage(b);
    });
  }
}

"What, WhatsApp supports it natively? It's named Broadcast Lists? Whoa..."

"Broadcast List" don't deliver messages if the sender contact is not in the recipient contact list.