Тестовый случай всегда терпит неудачу, потому что не может найти локатор элемента

const None =
  Symbol ()

const combinations = (...xs) =>
{ const loop = function* (comb, [x = None, ...xs])
  { if (x === None)
      return yield comb
    
    yield* loop ([...comb, x], xs)
    yield* loop (comb, xs)
  }
  return Array.from (loop ([], xs))
}

console.log (combinations ('a'))
// [ [a], [] ]

console.log (combinations ('a', 'b'))
// [ [a,b], [a], [b], [] ]

console.log (combinations ('a', 'b', 'c'))
// [ [a,b,c], [a,b], [a,c], [a], [b,c], [b], [c], [] ]