I'm trying to check the map key type to determine how i should filter it. My current approach is to check `myMap.keys().next().value` surprisingly this seems to be `undefined` regardless of whether its a string, int etc. 

I need to check if the key is either an integer or empty. So far i have tried this: 

```
!key.next().value // for no key
Number.isInteger(key.next().value) // for a numbered key

```

None of my if-statements are triggered with these checks.