Set select option 'selected', by value

To select an option with value 'val2':

$('.id_100 option[value=val2]').attr('selected','selected');

There's an easier way that doesn't require you to go into the options tag:

$("div.id_100 select").val("val2");

Check out the this jQuery method.

NOTE: The above code does not trigger the change event. You need to call it like this for full compatibility:

$("div.id_100 select").val("val2").change();