HTML Code

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>createTouch optional</title>
  <style>body{font-family:system-ui,sans-serif;padding:1.5rem;} pre{border:1px solid #ccc;padding:0.75rem;}</style>
</head>
<body>
  <button id="btn" type="button">Try optional args</button>
  <pre id="out">Click the button</pre>
  <script>
    document.getElementById("btn").addEventListener("click", function () {
      if (typeof document.createTouch !== "function") {
        document.getElementById("out").textContent =
          "createTouch unavailable — cannot demo optional args";
        return;
      }
      var bare = document.createTouch();
      var partial = document.createTouch(window, document.body, 3);
      document.getElementById("out").textContent = [
        "bare identifier: " + bare.identifier,
        "partial identifier: " + partial.identifier
      ].join("\n");
    });
  </script>
</body>
</html>

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Document.createTouch — optional args (Try It)