vk-mute/hide_element.js

// Returns false if there was an element not hidden
function hideElements(chatBody) {
    let idToHide;
    chrome.storage.sync.get('idToHide', function(data) {
        idToHide = data.idToHide;
    });

    let r = true;
    for (var item of chatBody.children) {
        if (item.dataset.peer === idToHide) {
            if (item.style.display !== "none") {
                item.style.display = "none";
                r = false;
            }
        }
    }
    return r;
}

let chatBody = document.getElementsByClassName("_im_peer_history im-page-chat-contain")[0];

chatBody.addEventListener('DOMNodeInserted', function(event) {
    if (event.target.className === 'im-mess-stack _im_mess_stack ') {
        let idToHide;
        chrome.storage.sync.get('idToHide', function(data) {
            idToHide = data.idToHide;
        });

        chrome.storage.sync.get('isExtensionOn', function(data) {
            if (data.isExtensionOn) {
                if (event.target.dataset.peer === idToHide) {
                    event.target.style.display = "none";
                }
            }
        });
    }
});

// Try to hide until successful. Needed for page refresh.
var hideInterval = setInterval(function () {
    const chatBody = document.getElementsByClassName("_im_peer_history im-page-chat-contain")[0];
    if (hideElements(chatBody)) {
        clearInterval(hideInterval);
    }
}, 200);