JSFiddle - React, Tailwind, and code Playground

HTML

<div>asdf</div>

CSS

.previous-image {
    color: #ff0000;
}

JavaScript

var firstImg, observerConfig, firstImgObserver;

firstImg = $("body").find("div").first();
observerConfig = {
    attributes: true,
    childList: true,
    characterData: true
};
firstImgObserver = new MutationObserver(function (mutations) {
    mutations.forEach(function (mutation) {
        var newVal = $(mutation.target).prop(mutation.attributeName);
        if (mutation.attributeName === "class") {
            console.log("MutationObserver class changed to", newVal);
        } else if (mutation.attributeName === "id") {
            console.log("MutationObserver id changed to", newVal);
        }
    });
});

firstImgObserver.observe(firstImg[0], observerConfig);
// later, you can stop observing
//observer.disconnect();

firstImg.on("DOMAttrModified", function (e) {
    var newVal = $(this).prop(e.originalEvent.attrName);
    console.log("DOMAttrModified", e.originalEvent.attrName, "changed to", newVal);
});

setTimeout(function () {
    firstImg.addClass("previous-image").addClass("fdsa");
}, 1000);