$('select').change(function(){
  $('option:selected').each(function(){
    alert( $(this).text() );
  });
});

select{
    overflow:auto;
    width: 150px;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/2.2.4/jquery.min.js"></script>
<select id="the_select" size="5" multiple>
  <option>Bob</option>
  <option>John</option>
  <option>Sam</option>
  <option>Jason</option>
  <option>Sarah</option>
</select>