Calculators.js

ui = {

   initPage: function () {        
       //Calculator       
       var newInput = "<input type='number' class='input_amount target' value='1' max='50000' min= />";
       ($('#input_amount')).html(newInput);
       var amountsArray = [];
       $('.item_number').each(function(index, element){
           amountsArray[index] = parseInt($(element).text());
       })
        $(".input_amount").on('change', function() {
           var inputValue = $('.input_amount').val();
           if(inputValue>9999){
             $('.input_amount').val(9999);
             inputValue = 9999;
           }

           if (!isNaN(inputValue) && inputValue > 0) {
               $('.item_number').each(function(index, element){
                   $(element).text(amountsArray[index] * inputValue);
               });
           } else {
               $('.item_number').each(function(index, element){
                   $(element).text(amountsArray[index]);
               });
           }
       });
   },
   
 init: function () {
       ui.initPage();
   }

}

ui.init();