Show javascript var result in text box

<input type="text" id="item-price">

   var basePrice = 0;

   $(document).ready(function() {
       $(".calculate").change(function() {
           newPrice = basePrice;
           $(".calculate option:selected").each(function() {
               newPrice += $(this).data('price')
           });
           $("#item-price").val(newPrice.toFixed(2));
    });
});