Set select option 'selected', by value

Question

I have a select field with some options in it. Now I need to select one of those options with jQuery. But how can I do that when I only know the

Answer 1

Deselect all first and filter the selectable options:

$('.id_100 option')
     .removeAttr('selected')
     .filter('[value=val1]')
         .attr('selected', true)