HTML Code

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>animationend cleanup</title>
  <style>
    #box {
      width: 80px;
      height: 80px;
      background: #dc2626;
      margin-bottom: 0.75rem;
    }
    #box.bounce {
      animation: bounce 0.6s ease 1;
    }
    @keyframes bounce {
      0% { transform: translateY(0); }
      50% { transform: translateY(-24px); }
      100% { transform: translateY(0); }
    }
  </style>
</head>
<body>
  <div id="box"></div>
  <button id="play" type="button">Play</button>
  <pre id="out">Click Play</pre>
  <script>
    var box = document.getElementById("box");
    var btn = document.getElementById("play");
    var out = document.getElementById("out");

    box.addEventListener("animationend", function () {
      box.classList.remove("bounce");
      out.textContent = "Class removed after animationend";
    });

    btn.addEventListener("click", function () {
      out.textContent = "Animating...";
      box.classList.add("bounce");
    });

    btn.click();
  </script>
</body>
</html>

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Element animationend — cleanup class (Try It)