<!DOCTYPE html>
<html>
<head>
  <script>
    function validateForm() {
      let x = document.forms["nameForm"]["name"].value;
      if (x == "") {
        alert("Name must be filled out");
        return false;
      }
    }
  </script>
</head>
<body>

  <h2>JavaScript Validation</h2>

  <form name="nameForm" action="" onsubmit="return validateForm()" method="post">
    Name: <input type="text" name="name">
    <input type="submit" value="Submit">
  </form>

</body>
</html>