WhatsApp web reply using keyboard

ww-reply.js

// ==UserScript==
// @name         whatsapp-web-reply
// @namespace    https://yoogottamk.github.io/
// @version      0.1
// @description  reply to messages using keyboard shortcuts alt+{up,down}
// @author       yoogottamk
// @match        https://web.whatsapp.com/
// @grant        none
// ==/UserScript==

(function () {
  'use strict';
  const getMessages = () => document.querySelectorAll(".message-in, .message-out"),
    getDoubleClickEvent = () => {
      let clickEvent = document.createEvent('MouseEvents');
      clickEvent.initEvent('dblclick', true, true);
      return clickEvent;
    },
    getMessageIdFromDOMAttributes = messageNode => messageNode.dataset.id.split("_")[2],
    selectRelativeMessage = relativeDistance => () => {
      const messageList = getMessages(),
        messageIds = Array.from(messageList).map(getMessageIdFromDOMAttributes),
        newMessageIndex = messageIds.findIndex(mId => mId == lastSelectedMessageId) + relativeDistance;

      let selectedMessage;

      if (!lastSelectedMessageId || newMessageIndex < 0 || newMessageIndex >= messageList.length)
        selectedMessage = messageList[messageList.length - 1];
      else
        selectedMessage = messageList[newMessageIndex];

      lastSelectedMessageId = getMessageIdFromDOMAttributes(selectedMessage);

      selectedMessage.dispatchEvent(getDoubleClickEvent());
      selectedMessage.scrollIntoView();
    },
    selectPreviousMessage = selectRelativeMessage(-1),
    selectNextMessage = selectRelativeMessage(1);

  let lastSelectedMessageId;

  document.addEventListener("keydown", e => {
    // 38 is up, 40 is down
    if (e.keyCode == 38 && e.altKey) {
      selectPreviousMessage();
      e.stopPropagation();
    } else if (e.keyCode == 40 && e.altKey) {
      selectNextMessage();
      e.stopPropagation();
    }

    // escape
    if (e.keyCode == 27) {
      lastSelectedMessageId = null;
    }
  }, true);
})();