Function isDefaultContext

isDefaultContext(contextId): boolean
JMap.MapContext.isDefaultContext

Returns true if the map context is the default one, given the id.

The default map context is loaded automatically at startup.
Parameters
- contextId: JId
  the JMap map context id
Returns boolean
Throws
if map-context not found

Example
```
// returns true if the map context id=3 is the default one.
JMap.MapContext.isDefaultContext(3)
```