[drop-down-menu] Check if value is in select list with JQuery

Why not use a filter?

var thevalue = 'foo';    
var exists = $('#select-box option').filter(function(){ return $(this).val() == thevalue; }).length;

Loose comparisons work because exists > 0 is true, exists == 0 is false, so you can just use

if(exists){
    // it is in the dropdown
}

Or combine it:

if($('#select-box option').filter(function(){ return $(this).val() == thevalue; }).length){
    // found
}

Or where each select dropdown has the select-boxes class this will give you a jquery object of the select(s) which contain the value:

var matched = $('.select-boxes option').filter(function(){ return $(this).val() == thevalue; }).parent();