I have an observer that does a check for the existence of an element in the DOM. And also, inside observer I have a fetch request which doesn't work.

Please help with the code, or explain why it doesn't work. If I make this fetch query outside of observer, it works fine.

let observer = new MutationObserver(() => {
    if (document.querySelector("any_selector")) {

        let options = {
            method: "GET",
            headers: { Accept: "application/json", "Content-Type": "application/json" },
        };

        fetch('https://any_url', options)
            .then((response) => response.json())
            .then(get_any_data);

        function get_any_data(data) {
            console.log("Work!!!");
        }

        observer.disconnect();
    }
});
observer.observe(document.querySelector("body"), { childList: true });