Userscript to keep youtube chat to "live chat" (instead of "top chat")

livechatpusher.js

// ==UserScript==
// @name         YouTube Persistent Live Chat
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  Try to keep youtube livestream chat in "live chat" or "live chat replay" mode
// @include      https://www.youtube.com/*
// @icon         data:image/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==
// @grant        none
// ==/UserScript==

(function() {
    'use strict';

    const timeout = 100; // milliseconds between attempt
    let timeoutID;

    // returns the livechat iframe document
    function getChatDoc() {
        const theFrame = document.querySelector("#chat iframe");
        if (theFrame && theFrame.contentWindow && theFrame.contentWindow.document) {
            return theFrame.contentWindow.document;
        }
    }

    // returns true if we have a live chat header
    function isLiveChat() {
        const frameDoc = getChatDoc();
        const theHeader = (frameDoc || document).querySelector('div.yt-dropdown-menu#label-text')
        if (!theHeader) {
            return false;
        }
        return /live chat/i.test(theHeader.innerText);
    }

    // keep trying the clicker every few milliseconds until we have the live chat header
    function tryClicker() {
        if (isLiveChat()) {
            // stop trying on success
            clearTimeout(timeoutID);
        } else {
            // else, try again and reset timer
            liveChatClick();
            timeoutID = setTimeout(tryClicker, timeout);
        }
    }

    // clicks the "live chat" or "live chat replay" button
    function liveChatClick() {
        const frameDoc = getChatDoc();
        const theitems = (frameDoc || document).querySelectorAll('div.yt-dropdown-menu.item')
        for (const item of theitems) {
            if (/live chat/i.test(item.innerText)) {
                item.click();
            }
        }
    }

     window.addEventListener("resize", tryClicker);
     window.addEventListener("load", tryClicker);

})();