LeetCode kth smallest using Generator(JS)

kth.gen.js

function* gen(g) {
  yield* g
}

function kth(k, g) {
  while (k-- > 0) g.next()  // 문제는 1부터라 0대신 1
  return g.next().value
}

function* merge(g1, g2) {
  let n1 = g1.next()
  let n2 = g2.next()
  while (!n1.done && !n2.done) {
    if (n1.value < n2.value) {
      yield n1.value
      n1 = g1.next()
    } else {
      yield n2.value
      n2 = g2.next()
    }
  }
  if (!n1.done) {
    yield n1.value
    yield* g1
  }
  if (!n2.done) {
    yield n2.value
    yield* g2
  }
}

var kthSmallest = function (matrix, k) {
return kth(k, matrix.map(gen).reduce(merge));
};