How to set the first option on a select box using jQuery?

Something like this should do the trick: https://jsfiddle.net/TmJCE/898/

$('#name2').change(function(){
    $('#name').prop('selectedIndex',0);
});


$('#name').change(function(){
    $('#name2').prop('selectedIndex',0);
});

If you just want to reset the select element to it's first position, the simplest way may be:

$('#name2').val('');

To reset all select elements in the document:

$('select').val('')

EDIT: To clarify as per a comment below, this resets the select element to its first blank entry and only if a blank entry exists in the list.

As pointed out by @PierredeLESPINAY in the comments, my original solution was incorrect - it would reset the dropdown to the topmost option, but only because the undefined return value resolved to index 0.

Here's a correct solution, which takes the selected property into account:

$('#name').change(function(){
    $('#name2').val(function () {
        return $(this).find('option').filter(function () {
            return $(this).prop('defaultSelected');
        }).val();
    });
});

DEMO: http://jsfiddle.net/weg82/257/

Original answer - INCORRECT

In jQuery 1.6+ you need to use the .prop method to get the default selection:

// Resets the name2 dropdown to its default value
$('#name2').val( $('#name2').prop('defaultSelected') );

To make it reset dynamically when the first dropdown changes, use the .change event:

$('#name').change(function(){
  $('#name2').val( $('#name2').prop('defaultSelected') );
});