Javascript: Unexprected Symbol.iterator

Lets validate some data, and lets do some smart checks with a unknown random schema. Lets same why wnat to check internal id references, and of course internal ids wil be in iternal things, lets assume arrays for now:

for (collection of Object.values(data)) {
  for (i of collection) {
    for (field of Object.values(i)) {
      for (item of field) {
        // check item.id
      }
    }
  }
}

But someone decided to wrap arrays into classes because, lets be honest, pure json inside js never stays pure. So lets check the iterator symbol magic:

for (field of Object.values(i)) {
  if (!field[Symbol.iterator]) continue;
  for (item of field) {
    // check item.id
  }
}

Perferct, but wait... why the item takes values of single letter strings. Oh wait, dont tell me that this is a thing:

"test"[Symbol.iterator]

Yes it is, so lets add it to the condition:

typeof field === "string" || !field[Symbol.iterator]

done_