Hackerrank: The Birthday Bar Solution

1function birthday(s, d, m) {
2  let res = 0
3  const sum = arr => arr.reduce((acc, el) => acc + el, 0)
4  for (let i = 0; i < s.length - m + 1; i++) {
5    if (sum(s.slice(i, i + m)) === d) {
6      res++
7    }
8  }
9  return res
10}