Function getLayerAttribute

getLayerAttribute(layerId, attributeName): JLayerAttribute
JMap.Layer.getLayerAttribute

Returns the attribute descriptor for a given layer and attribute
Parameters
- layerId: JId
  The JMap layer id
- attributeName: string
  The JMap attribute name
Returns JLayerAttribute
Throws
Error if layer or attribute not found

Example
```
 // returns the layer attribute descriptor
 JMap.Layer.getLayerAttribute(4, "SPECIES")
```