Function existsById

existsById(basemapId): boolean
JMap.Map.Basemap.existsById

Returs true if basemap exist for the given id.
Parameters
- basemapId: string
  The basemap id, use JMap.Map.Basemap.getAllId() to get available basemap ids
Returns boolean
Example
```
// returns true if "streets" basemap exist
JMap.Map.Basemap.existsById("streets")
```