มีปัญหา Javascript คำนวณค่าโดยใช้ .change() แล้วมีปัญหานิดหน่อยครับ

$(document).ready(function() {
   $('input[name=amount],select[name=posttype]').change(function(e)  {
        var amount = $(this).val();
        var weight = amount*100;
       
       if($('select[name=posttype]').val()=='ems'){
        $.post('test.php?action=ems', {'weight':weight}, function(data) {
            var getamount = data;
            $("input[name=postprice]").val(getamount-0);
            var emsprice = $("input[name=postprice]").val();
                var total = parseFloat(parseFloat(amount)*35)+parseFloat(emsprice);
            $("input[name=price]").val(total);
        });
       }
       
       else if($('select[name=posttype]').val()=='normal'){
        $.post('test.php?action=normal', {'weight':weight}, function(data) {
            var getamount = data;
            $("input[name=postprice]").val(getamount-0);
            var emsprice = $("input[name=postprice]").val();
                var total = parseFloat(parseFloat(amount)*35)+parseFloat(emsprice);
            $("input[name=price]").val(total);
        });
       }

    });
   });