js检测dom元素的变化

    new MutationObserver((mutations, observer) => {
    const el = document.querySelector("span.Title-followNum");
    if (el) {
        observer.disconnect()
        new MutationObserver((mutations, observer) => {
            debugger
        }).observe(el, {
            childList: true,
            subtree: true
        })
    }
}).observe(document, {
    childList: true,
    subtree: true
})