Function hasKeyValue

hasKeyValue<K, V>(
    map: ReadonlyMap<K, V>,
    key: K,
    value: V,
    comparer: IsEqual<V>,
): boolean
Returns true if map contains value under key, using comparer function. Use hasAnyValue if you don't care what key value might be under.

Having a comparer function is useful to check by value rather than object reference.
Type Parameters
- K
- V
Parameters
- map: ReadonlyMap<K, V>
  Map to search
- key: K
  Key to search
- value: V
  Value to search
- comparer: IsEqual<V>
  Function to determine match
Returns boolean
True if key is found
Example: Find key value based on string equality
```
hasKeyValue(map,`hello`, `samantha`, (a, b) => a === b);
```