R runZoned<R>(R body(), { Map zoneValues, ZoneSpecification zoneSpecification, Function onError })

Runs body in its own zone.

If onError is non-null the zone is considered an error zone. All uncaught errors, synchronous or asynchronous, in the zone are caught and handled by the callback.

Errors may never cross error-zone boundaries. This is intuitive for leaving a zone, but it also applies for errors that would enter an error-zone. Errors that try to cross error-zone boundaries are considered uncaught.

var future = new Future.value(499);
runZoned(() {
  future = future.then((_) { throw "error in first error-zone"; });
  runZoned(() {
    future = future.catchError((e) { print("Never reached!"); });
  }, onError: (e) { print("unused error handler"); });
}, onError: (e) { print("catches error of first error-zone."); });

Example:

runZoned(() {
  new Future(() { throw "asynchronous error"; });
}, onError: print);  // Will print "asynchronous error".

Source 

R runZoned<R>(R body(),
    {Map zoneValues, ZoneSpecification zoneSpecification, Function onError}) {
  HandleUncaughtErrorHandler errorHandler;
  if (onError != null) {
    errorHandler = (Zone self, ZoneDelegate parent, Zone zone, error,
        StackTrace stackTrace) {
      try {
        if (onError is ZoneBinaryCallback<R, Object, StackTrace>) {
          return self.parent.runBinary(onError, error, stackTrace);
        }
        return self.parent.runUnary(onError, error);
      } catch (e, s) {
        if (identical(e, error)) {
          return parent.handleUncaughtError(zone, error, stackTrace);
        } else {
          return parent.handleUncaughtError(zone, e, s);
        }
      }
    };
  }
  if (zoneSpecification == null) {
    zoneSpecification =
        new ZoneSpecification(handleUncaughtError: errorHandler);
  } else if (errorHandler != null) {
    zoneSpecification = new ZoneSpecification.from(zoneSpecification,
        handleUncaughtError: errorHandler);
  }
  Zone zone = Zone.current
      .fork(specification: zoneSpecification, zoneValues: zoneValues);
  if (onError != null) {
    return zone.runGuarded(body);
  } else {
    return zone.run(body);
  }
}