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 set select value

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

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);
}