RocketChat/Rocket.Chat

export const waitForElement = async <TElement extends Element>(
    selector: string,
    { parent = document.documentElement, signal }: { parent?: Element; signal?: AbortSignal } = {},
): Promise<TElement> => {
    const element = parent.querySelector<TElement>(selector);
    return new Promise((resolve, reject) => {
        if (element) {
            return resolve(element);
        }
        const observer = new MutationObserver((_, obs) => {
            const element = parent.querySelector<TElement>(selector);
            if (element) {
                obs.disconnect(); // stop observing
                return resolve(element);
            }
        });
        observer.observe(parent, {
            childList: true,
            subtree: true,
        });

        signal?.addEventListener('abort', () => {
            observer.disconnect();
            reject(new DOMException('Aborted', 'AbortError'));
        });
    });
};