Uncaught TypeError: Cannot read property 'value' of undefined after querySelectorAll

I am working on a javascript and getting some error. I am using jquery repeater to catch some repeatable products.

$(document).on('keyup', '#discount', function(){
   var name = $(this).attr('name');
   var loopNo = document.querySelectorAll('.count_list .list_repeat').length;
   var i;
   var sum = 0;
   for(i=0;i<=loopNo;i++){
       var selling_price = parseInt(document.getElementsByName("sell_products[".concat(i).concat("][selling_price]"))[0].value);

       var quantity = parseInt(document.getElementsByName("sell_products[".concat(i).concat
    ("][quantity]"))[0].value);

       var selling_price_quantity = selling_price * quantity;

       sum = sum + (selling_price_quantity - parseInt(document.getElementsByName("sell_products[".concat(i).concat("][discount]"))[0].value));

}
   document.getElementById('total_amount').innerHTML = sum;    });

This is the code for what I want to get but I am getting Uncaught TypeError: Cannot read property 'value' of undefined this error. I am not able to solve it. Here you can get the full codes. http://ift.tt/2wU2iq6 . Can anyone please help?

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