defriz

const sum = Array.prototype.reduce.call(
  document.querySelectorAll('[name^=AR_AMOUNT]'),
  (acc, n) => acc + +n.value,
  0
);

const sum = eval(Array
  .from(document.querySelectorAll('[name^=AR_AMOUNT]'), n => n.value)
  .join('+')
) ?? 0;

const sum = (function sum(arr, index) {
  return arr[index] ? +arr[index].value + sum(arr, index + 1) : 0;
})(document.querySelectorAll('[name^=AR_AMOUNT]'), 0);