HTML Code

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>cancelBubble false</title>
  <style>
    #parent { padding: 16px; border: 2px solid #ca8a04; background: #fefce8; }
    #child { padding: 12px; border: 2px dashed #2563eb; margin-top: 8px; }
  </style>
</head>
<body>
  <div id="parent">Parent
    <div id="child">Child</div>
  </div>
  <button id="fire" type="button">Dispatch with cancelBubble = false</button>
  <pre id="out">Waiting...</pre>
  <script>
    var parent = document.getElementById("parent");
    var child = document.getElementById("child");
    var out = document.getElementById("out");

    document.getElementById("fire").onclick = function () {
      var heard = false;
      function onParent() { heard = true; }
      function onChild(e) { e.cancelBubble = false; }
      parent.addEventListener("ping", onParent);
      child.addEventListener("ping", onChild);
      child.dispatchEvent(new Event("ping", { bubbles: true }));
      parent.removeEventListener("ping", onParent);
      child.removeEventListener("ping", onChild);
      out.textContent = heard
        ? "parent still heard it"
        : "parent did not hear it";
    };
  </script>
</body>
</html>

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Event.cancelBubble — false is a no-op (Try It)