Interface ErrorFirstCallback<T>
interface ErrorFirstCallback<T> {     (err, 
result?): void;     (err, 
result): void; }   - ErrorFirstCallback(err, result?): void
- Parameters- err: any
- Optionalresult: null
 
- Returns void
- ErrorFirstCallback(err, result): void
- Parameters- err: undefined | null
- result: T
 
- Returns void
An interface for error handling callbacks (blockchain event handler).