hwo to set a dropdown value over another default value in js code example

Example: html select specify deafult select by js variable

$(function() {
    var temp="a"; 
    $("#MySelect").val(temp);
});

<select name="MySelect" id="MySelect">
    <option value="a">a</option>
    <option value="b">b</option>
    <option value="c">c</option>
</select>