안녕하세요, reduce 함수의 사용법에 질문드리고 싶습니다

const _reduce = (fns, acc, iter) => {
  if(!iter){
    iter = acc[Symbol.iterator]();
    acc = iter.next().value;
  }
  for (const a of iter){
    acc = fns(acc, a);
  }
  return acc
};

console.log(
  _reduce(
    (total_price, product) => total_price + product.price, 
    0,
     products)
);