Javascript validation

I'm trying to get the "Javascript Validation" to work from the "Contact form" section of this site. I'm using my own Contact form and when I add the javascript script and then test it out I get the "This field is required." but the script isn't working for the subject section of the form. Any help would be greatly appreciated! My code:

<div class="contact-us-info">
        <div class="container">
            <div class="row">
                <div class="col-lg-8 message">
                    <h3>Send us a message</h3>
                    <p>
                        You can contact us with anything related to Devcde. <br/> We'll get in touch with you as soon as possible.
                    </p>
                    <form role="form" id="contact-form" action="mail.php" method="POST">
                        <div class="form-group">
                            <label for="name">Your name</label>
                            <input type="text" name="name" class="form-control" id="name" />
                        </div>
                        <div class="form-group">
                            <label for="email">Email address</label>
                            <input type="email" name="email" class="form-control" id="email" />
                        </div>
                        <div class="form-group">
                            <label for="subject">Subject</label>
                            <input type="text" name="subject" class="form-control" id="subject" />
                        </div>
                        <div class="form-group">
                            <label for="message">Your message</label>
                            <textarea name="message" class="form-control" id="message" rows="6"></textarea>
                        </div>
                        <div class="submit">
                            <input type="submit" class="button button-small" onclick="validateForm()" value="Email us" />
                        </div>
                    </form>
                    <script>
  function validateForm() {
  var name =  document.getElementById('name').value;
  if (name == "") {
      document.getElementById('status').innerHTML = "Name cannot be empty";
      return false;
  }
  var email =  document.getElementById('email').value;
  if (email == "") {
      document.getElementById('status').innerHTML = "Email cannot be empty";
      return false;
  } else {
      var re = /^(([^<>()\[\]\\.,;:\s@"]+(\.[^<>()\[\]\\.,;:\s@"]+)*)|(".+"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/;
      if(!re.test(email)){
          document.getElementById('status').innerHTML = "Email format invalid";
          return false;
      }
  }
  var subject =  document.getElementById('subject').value;
  if (subject == "") {
      document.getElementById('status').innerHTML = "Subject cannot be empty";
      return false;
  }
  var message =  document.getElementById('message').value;
  if (message == "") {
      document.getElementById('status').innerHTML = "Message cannot be empty";
      return false;
  }
  document.getElementById('status').innerHTML = "Sending...";
  document.getElementById('contact-form').submit();

  }
</script>