Function thematicAddition

thematicAddition(listenerId, fn): void
JMap.Event.Layer.on.thematicAddition

This event is triggered when a custom thematic is added.
Parameters
- listenerId: string
  Your listener id (must be unique for all layer events)
- fn: ((params) => void)
  Your listener function
  - - (params): void
    - Parameters
      params: JAddMapThematicEventParams
      Returns void
Returns void
Example
```
// Each time a custom thematic is added, will display a message in the console
JMap.Event.Layer.on.thematicAddition(
   "custom-thematic-addition",
   params => {
     console.log(`Thematic has been added for layer id="${params.layerId}". Params: `, params)
   }
)
```