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<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>promise() encapsulation</title>
</head>
<body>
  <h1>Return promise(), keep Deferred private</h1>
  <button id="run">Run task</button>
  <pre id="out"></pre>
  <script src="https://code.jquery.com/jquery-3.7.1.min.js"></script>
  <script>
    function loadConfig() {
      var dfd = $.Deferred();

      setTimeout(function () {
        dfd.resolve({ theme: "dark", lang: "en" });
      }, 500);

      return dfd.promise();
    }

    $("#run").on("click", function () {
      var lines = [];
      loadConfig().done(function (cfg) {
        lines.push("theme: " + cfg.theme);
        lines.push("lang: " + cfg.lang);
        document.getElementById("out").textContent = lines.join("\n");
      });
    });
  </script>
</body>
</html>

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jQuery.Deferred() — return promise() (Try It)