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<html lang="en">

<head>

  <meta charset="utf-8">

  <title>$.Callbacks("once")</title>

</head>

<body>

  <h1>once flag</h1>

  <pre id="out"></pre>

  <script src="https://code.jquery.com/jquery-3.7.1.min.js"></script>

  <script>

    (function () {

      var lines = [];

      var callbacks = $.Callbacks("once");



      callbacks.add(function () {

        lines.push("Runs on first fire only");

      });



      callbacks.fire();

      callbacks.fire();

      document.getElementById("out").textContent = lines.join("\n");

    })();

  </script>

</body>

</html>

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jQuery $.Callbacks() — once flag (Try It)