Q:

Processing select form value with JS

I have a very simple form:
  <form id="signup">
     <div class="form-group">
         <input type="text" name="email" placeholder="Email" id="email" required>
     </div>

     <div class="form-group">
         <input type="text" name="tn" placeholder="tn" required>
      </div>

      <div class="form-group">
          <input type="text" name="em" placeholder="em" id="em" required>                                   
      </div>

      <button type="submit" class="btn">Submit</button>
</form>

This is process by a small js file:
$(function() {

    var form = $('#signup');
    var formMessages = $('#form');

    $(form).submit(function(e) {
       e.preventDefault();
        $('#thanks').hide();
        var formData = {
            'trackingnumber'    : $('input[name=email]').val(),
            'email'             : $('input[name=courier]').val(),
            'courier'           : $('input[name=em]').val(),
        };

        // process the form
        $.ajax({
            type        : 'POST', 
            url         : 'signup.php', 
            data        : formData, 
            dataType    : 'json'
        }) 
        .done(function(data) {
            console.log(data); 
        });

    });

});

I am looking to change the input for 'em' to an drop down box using select.
<div class="form-group">
     <input type="text" name="em" placeholder="em" id="em" required>
         <select name="em">
             <option value="1">Saab</option>
             <option value="2">Rover</option>
             <option value="3">Daewoo</option>
             <option value="4">Ford</option>
             <option value="5">Peugeot</option>
         </select>
</div>

How do I access the value in the JS file?
I tried changing the line from:
'courier'           : $('input[name=em]').val(),

to
'courier'           : $('select[name=em]').val(),

but it doesn't appear to be working.

A:

Description
To make this code runnable I changed it from a form to a div, I also had to change .submit to .on('click', not huge changes.
A select in html doesn't need to be wrapped with an input, because it was wrapped (and not encapsulated <input><select></select></input> it didn't work as you were expecting.  The below html should work fine.
Changes
JS
'courier': $('select[name=em]').val(),

HTML
<div class="form-group">
  <select name="em" required>
     <option value="1">Saab</option>
     <option value="2">Rover</option>
     <option value="3">Daewoo</option>
     <option value="4">Ford</option>
     <option value="5">Peugeot</option>
  </select>
</div>

Live Example

$(function() {

  var form = $('#signup');
  var formMessages = $('#form');

  $('#signup .btn').on('click', function(e) {
    e.preventDefault();
    $('#thanks').hide();
    var formData = {
      'trackingnumber': $('input[name=email]').val(),
      'email': $('input[name=courier]').val(),
      'courier': $('select[name=em]').val(),
    };

    console.log(formData);
  });
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.0/jquery.min.js"></script>
<div id="signup">
  <div class="form-group">
    <input type="text" name="email" placeholder="Email" id="email" required>
  </div>

  <div class="form-group">
    <input type="text" name="tn" placeholder="tn" required>
  </div>

  <div class="form-group">
    <select name="em" required>
             <option value="1">Saab</option>
             <option value="2">Rover</option>
             <option value="3">Daewoo</option>
             <option value="4">Ford</option>
             <option value="5">Peugeot</option>
         </select>
  </div>

  <button type="submit" class="btn">Submit</button>
</div>

