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<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>reject() — validation</title>
</head>
<body>
  <h1>saveUser validation</h1>
  <input id="name" type="text" value="A" placeholder="Name">
  <button id="save">Save</button>
  <pre id="out">Enter a name and save...</pre>
  <script src="https://code.jquery.com/jquery-3.7.1.min.js"></script>
  <script>
    function saveUser(name) {
      var dfd = $.Deferred();
      if (!name || name.length < 2) {
        dfd.reject("Name must be at least 2 characters");
      } else {
        dfd.resolve({ saved: true, name: name });
      }
      return dfd.promise();
    }

    $("#save").on("click", function () {
      var name = $("#name").val();
      saveUser(name).then(function (result) {
        document.getElementById("out").textContent =
          "Saved: " + result.name;
      }).catch(function (err) {
        document.getElementById("out").textContent =
          "Save failed: " + err;
      });
    });
  </script>
</body>
</html>

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jQuery deferred.reject() — validation API (Try It)