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

While I'm not sure about exactly what you want to accomplish, this bit of code worked for me.

<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>

No need to use jQuery for this:

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

lencioni's answer is what I'd recommend. You can change the selector for the option ('#mySelect option:last') to select the option with a specific value using "#mySelect option[value='yourDefaultValue']". More on selectors.

If you're working extensively with select lists on the client check out this plugin: http://www.texotela.co.uk/code/jquery/select/. Take a look the source if you want to see some more examples of working with select lists.

I already came across the texotela plugin mentioned, which let me solve it like this:

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

Look at the selectedIndex of the select element. BTW, that's a plain ol' DOM thing, not JQuery-specific.

$("#select_box_id").children()[1].selected

This is another way of checking an option is selected or not in jquery. This will return Boolean (True or False).

[1] is index of select box option