Check if option is selected with jQuery, if not select a default

<select id="mySelect" multiple="multiple">
  <option value="1">First</option>
  <option value="2">Second</option>
  <option value="3">Third</option>
  <option value="4">Fourth</option>
</select>

<script type="text/javascript">
$(document).ready(function() {
  if (!$("#mySelect option:selected").length)
    $("#mySelect option[value='3']").attr('selected', 'selected');
});
</script>

var foo = document.getElementById('yourSelect');
if (foo)
{
   if (foo.selectedIndex != null)
   {
       foo.selectedIndex = 0;
   }
}

function selectOption(select_id, option_val) {
    $('#'+select_id+' option:selected').removeAttr('selected');
    $('#'+select_id+' option[value='+option_val+']').attr('selected','selected');
}

<script type="text/javascript">
$(document).ready(function() {
  if (!$("#mySelect option:selected").length)
   $("#mySelect").val( 3 );

});
</script>

$("#mySelect").val( 3 );

$(".Result").html($("option:selected").text());

$(document).ready(function(){
    if ( $("#context").selectedValues() == false) {
    $("#context").selectOptions("71");
    }
});

$("option[value*='2']").attr('selected', 'selected');
// 2 for example, add * for every option