HTML Code

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>composed open closed</title>
  <style>
    open-shadow, closed-shadow {
      display: block;
      margin: 8px 0;
      padding: 8px;
      border: 1px solid #ccc;
      cursor: pointer;
    }
  </style>
</head>
<body>
  <open-shadow text="I have an open shadow root"></open-shadow>
  <closed-shadow text="I have a closed shadow root"></closed-shadow>
  <pre id="out">Click a custom element...</pre>
  <script>
    customElements.define("open-shadow", class extends HTMLElement {
      constructor() {
        super();
        var p = document.createElement("p");
        p.textContent = this.getAttribute("text");
        this.attachShadow({ mode: "open" }).appendChild(p);
      }
    });

    customElements.define("closed-shadow", class extends HTMLElement {
      constructor() {
        super();
        var p = document.createElement("p");
        p.textContent = this.getAttribute("text");
        this.attachShadow({ mode: "closed" }).appendChild(p);
      }
    });

    document.querySelector("html").addEventListener("click", function (e) {
      var names = e.composedPath().map(function (n) {
        return n.nodeName || String(n);
      });
      document.getElementById("out").textContent =
        "composed = " + e.composed + "\n" +
        "path: " + names.slice(0, 6).join(" → ") +
        (names.length > 6 ? " → …" : "");
    });
  </script>
</body>
</html>

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Event.composed — open vs closed shadow (Try It)