pascal.js

function scan(fn, list, result = []) {
  if (list.length < 2)
    return result

  const [a, b, ...rest] = list

  return scan(fn, [b, ...rest], [...result, fn(a, b)])
}

function* pascal(row = [1]) {
  yield row

  if (row.length === 1)
    yield row = [...row, ...row]

  while (true) {
    yield row = [row[0], ...scan(add, row), row[0]]
  }
}

const add = (a, b) => a + b

const gen = pascal([7])
console.log(gen.next())
console.log(gen.next())
console.log(gen.next())
console.log(gen.next())
console.log(gen.next())