问hasClass() jquery只工作一次

EN

$(document).ready(() => {
  //we define our observed element
  const observedElement = document.getElementById("first-item");
  //we create an observer and pass a callback function..
  new MutationObserver(mutationCallback)
    //and we set it to observe,a specific element's mutations
    .observe(observedElement, {
      attributes: true,
      attributeFilter: ["class"],
    });
  //it will run the callback function everytime it detects a mutation on the observed element..
  //such as change of classlist items etc..
});

const mutationCallback = () => {
  if ($("#first-item").hasClass("active")) {
    $(".go-prev").addClass("hideMe");
  } else {
    $(".go-prev").removeClass("hideMe");
  }
};

//lets make a mutation to observed element to see if it works
const testMutation = () => {
  $("#first-item").addClass("active");
}

.hideMe{
  display: none;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<h1 id="first-item">OBSERVED ELEMENT</h1>
<h1 class="go-prev">AFFECTED ELEMENT</h1>
<button onclick="testMutation()">TEST</button>