Function getById

getById(layerId, featureId): Promise<GeoJSON.Feature>
JMap.Feature.getById

Returns the feature (EPSG:4326 projection) for the given layer and feature id.
Parameters
- layerId: JId
  the JMap layer id
- featureId: JId
  the JMap feature id
Returns Promise<GeoJSON.Feature>
Throws
if layer or feature not found

Example
```
// returns the feature of layer id="3" and feature id="4"
JMap.Feature
 .getById(3, 4)
 .then(feature => console.info("Feature has been fetched", feature))
 .catch(error => console.error("An error occured", error))
```