JAP Destroyer v9002

// JAP Destroyer v9002
//
// Removes non-English chat messages and superchat in YouTube live chat
//
// v9002: this
//   - Fixed messages not appearing after some time
//   - Fixed chat scrolling
//   - Removed printing of filtered messages as otherwise they would be duplicated over and over
// v9001: https://pastebin.com/uj4rVWa6
//   - Modified and improved version of EOP Destroyer https://pastebin.com/XpiKsr8T
//     (it didn't support superchats and removed number-only messages)

javascript:(() => {
    let ALLOWED_MESSAGES = [""]; /*In lower case*/
    let FILTER_THRESHOLD = 85; /*How much % of the message should have english letters to not be filtered*/
    let func = () => {
        let chat_list = window.top.document.getElementById("chatframe")
            .contentDocument.querySelector("#items.style-scope.yt-live-chat-item-list-renderer");
        let observer = new MutationObserver((mutationsList, observer) => {
            let chat_items = chat_list.children;
            for(let i = 0; i < chat_items.length; i++) {
                let msgNode = chat_items[i].querySelector("#content #message");
                if(!msgNode)
                    continue;

                let msg = "";
                for(let i = 0; i < msgNode.childNodes.length; i++) {
                    let node = msgNode.childNodes[i];
                    if(node.nodeType === Node.TEXT_NODE) {
                        msg += node.nodeValue.trim();
                    }
                }
                if(!msg || ALLOWED_MESSAGES.includes(msg.toLowerCase()))
                    continue;

                let original = msg;
                msg = msg.replace(/[\^\(\)\[\]w\s.!?,\ufe0e]/g, "");
                if(msg.length === 0)
                    continue;

                let full_len = msg.length;
                let en_only_array = msg.match(/[a-z\d]+/gi);
                let en_len = en_only_array ? en_only_array.reduce((a, b) => a + b.length, 0) : 0;
                let percentage = en_len / full_len * 100;
                if(percentage < FILTER_THRESHOLD) {
                    chat_items[i].style.display = "none";
                } else {
                    chat_items[i].style.display = "";
                    let scroller = window.top.document.getElementById("chatframe").contentDocument.querySelector("#item-scroller");
                    scroller.scrollTop = scroller.scrollHeight;
                }
            }
        });

        observer.observe(chat_list, { attributes: false, childList: true, subtree: false });
    };

    if(window.top.document.readyState === "complete") {
        let chat_frame = window.top.document.getElementById("chatframe");
        let chat_doc = chat_frame.contentDocument;
        let chat_list = chat_doc.querySelector("#items.style-scope.yt-live-chat-item-list-renderer");
        if(chat_doc && chat_doc.readyState === "complete" && chat_list) {
            console.log("All loaded already");
            func();
        } else {
            console.log("Waiting for chat to load");
            chat_frame.contentWindow.addEventListener("load", func);
        }
    } else {
        console.log("Waiting for top to load");
        window.top.addEventListener("load", func);
    }
})();