YouTube chat subscription JavaScript: Get every new message during YouTube livestream chat with DOM Mutation Observer

YouTubeChatSubscribe.js

/*   YouTube Chat Subscription Function. Written by VityaSchel
 * Subscribe to new messages in YouTube chat in JS (browser-only)
 * Pass callback function which gets 2 parameters: author, message
 * !! Does not support emojies, user badges, message deletions !!
*/

function subscribeToChat(chatMessageCallback) {
    let chatObserverCallback = (mutationsList, observer) => {
        let messageMutation = mutationsList.filter(mutation => mutation.target.id === 'items').find(itemDOM => itemDOM.addedNodes.length > 0)
        if(messageMutation === undefined || messageMutation.addedNodes.length === 0) { return; }
        let messageNode = messageMutation.addedNodes[0]
        if(messageNode === undefined) { return; }
        let messageContent = messageNode.querySelector('#content')
        let authorName = messageContent.querySelector('yt-live-chat-author-chip > #author-name').innerText
        let messageText = messageContent.querySelector('#message').innerText
        chatMessageCallback(authorName, messageText)
    }
    let chatTarget = document.querySelector('yt-live-chat-item-list-renderer')
    let chatObserver = new MutationObserver(chatObserverCallback)
    chatObserver.observe(chatTarget, { childList: true, subtree: true })
}

// Example of usage:
// subscribeToChat((author, msg) => console.log(author, ':', msg))
/* Output:
 * Jay : pallavi Didi ️
 * Nightbot : Hey Sameer Kumar is Spammer randwa, enjoy The Good Life :)
*/

Tested in chat pop-up.
URL of chat pop-up: https://www.youtube.com/live_chat?is_popout=1&v=[VIDEO_ID]