var selvalues = $(this).val(); //["AS", "US", "CA"]

$('#countriesSelect').on('change', function(){

    var selvalues = $(this).val();

   console.log(selvalues .some(x => x !== 'US' && x == 'US'));

   if(selvalues.includes('US') || !selvalues.includes('US')){
        console.log('You cannot choose a foreign country when current selection is US');
    }
   if($.inArray("US",selvalues) != -1){
        $('#usregions').show().fadeIn();
        if($.inArray("US",selvalues) != -1){}
    } else {
        $('#usregions').hide().fadeOut();
    }
    $.each(selvalues, function( index, value ) {
        console.log()
        if(value == 'US' && value != 'US'){
            console.log('You cannot choose a foreign country when current selection is US');
        }
    });
});