Select2 demo

HTML

<script src="https://rawgit.com/select2/select2/master/dist/js/select2.js"></script>
<link rel="stylesheet" href="https://rawgit.com/select2/select2/master/dist/css/select2.min.css">
<form id="xform">

<select id="xselect">
  <option value="A" selected="selected">A</option>
  <option value="B">B</option>
  <option value="C">C</option>
</select>

<input type="email" class="input-text" name="test"  placeholder="" value="test">

</form>

<button onclick="trigger()">change</button>

JavaScript

$('#xselect').select2({
  placeholder: 'Select a letter'
});

var formFrom = document.querySelector('#xform');

formFrom.addEventListener('change', function(e) {
  console.log('input changed ');
  $('#xselect').trigger('change');
});

function trigger() {
  $('#xselect').val('C');
  $('#xselect').trigger('change');
}