Javascript nullish coalescing returns "f { [native code] }"

Question

I am getting an unexpected result while trying to use nullish coalescing operator on a return value that might be an array or might have an array as a child

  const storedKeys = await getStoreKeys();

  let keys = storedKeys.keys ?? storedKeys;
  console.log(keys);

console.log output:

ƒ keys() { [native code] }

Any idea on what might be going wrong? Thanks.

If `storedKeys` is an array, then `keys` is the array method that returns an iterator of its keys, or rather, indices, because it's an array. — kelsny, Aug 22 '22 at 18:33
@kelly, I think you mean if storedKeys is an Object or Map type. May be try invoking `storedKeys.keys()` with braces — MWaheed, Aug 22 '22 at 18:37
@MWaheed Arrays are objects, and thus they have a `keys` method as well. — kelsny, Aug 22 '22 at 18:38
Object has no "keys" method, at least not directly. Sure you can do Object.keys(someObj) but you can't do someObj.keys (undefined). — James, Aug 22 '22 at 18:42
Array has [`keys`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/keys?retiredLocale=uk) method, which logs into console — Mike, Aug 22 '22 at 18:48
Why do you think nullish coalescing has anything to do with this? — Ruan Mendes, Aug 22 '22 at 19:00

score 1 · Accepted Answer · answered Aug 22 '22 at 19:02

if storedObject is an array, it has a built-in keys() method (storedObject.keys() is equivalent to Object.keys(storedObject)). So the property isn't null, and it returns this function.

Use a ternary that checks if it's an array:

const storedKeys = Array.isArray(storedObject) ? storedObject : storedObject.keys;

Javascript nullish coalescing returns "f { [native code] }"

1 Answers1