함수형으로 map, filter, reduce만들기

map

 const products = [
    { name: '반팔티', price: 15000 },
    { name: '긴팔티', price: 20000 },
    { name: '핸드폰케이스', price: 15000 },
    { name: '후드티', price: 30000 },
    { name: '바지', price: 25000 }
  ];


const map = (f, iter) => {
	let res = [];
  for (const a of iter) {
    	res.push(f(a))
    }
  return res;
}

log(map((v) => v.name , products))

filter

const filter = (f, iter) => {
  let res = [];
  for (const a of iter) {
    if (f(a)) {
    	res.push(a);
    } 
  }
  return res;
}

log(filter((v)=>v.price < 20000, products))

reduce

const reduce = (f, acc, iter) => {
	if (!iter){
    	const iter = acc[Symbol.iterator]();
      	acc = iter.next().value;
    }
  	for (const a of iter ) {
    	acc = f(acc, a);
    }
  return acc;
}
const add = (a, b) => a + b;

log(reduce(add, 0, [1,2,3,4,5])) // 15 출력
log(reduce(add, [1,2,3,4,5])) // 15 출력

// 상품중에 20000이하의 상품의 전체 가격의 합 구하기
log(
reduce(add, 0, 
      filter((a) => a < 20000, 
         map((a) => a.price, products))
      )
) 
// 30000 출력