JAVASCRIPT

set select option as selected jquery

$(document).ready(function() {
    $("#gate option[value='Gateway 2']").prop('selected', true);
    // you need to specify id of combo to set right combo, if more than one combo
});

jquery change selected option

$('select option[value=8272]').attr('selected', '');

click select option to update div jquery

    $('#choose').change(function(event) {
        $.post('info.php', { selected: $('#choose').val() },
            function(data) {
                $('#update').html(data);
            }
        );            
    });

set selected option jquery

$("#id_of_select_input").val('value of option to set as selected');

change value on selected jquery

<select onchange="getval(this);">
    <option value="1">One</option>
    <option value="2">Two</option>
</select>
 Run code snippet

change value on selected jquery

function getval(sel)
{
    alert(sel.value);
}