Function getAllVisibleByLayerId

getAllVisibleByLayerId(layerId): JLayerThematic[]
JMap.Layer.Thematic.getAllVisibleByLayerId

Returns layer thematics that are currently displayed on the map.
Parameters
- layerId: JId
  The JMap layer id
Returns JLayerThematic[]
Throws
Error if no layer found for the id, or if the layer is a layer group.

Example
```
// returns the thematic(s) that are displayed on he map for layer id=4
JMap.Layer.Thematic.getAllVisibleByLayerId(4)
```