errorZone property Null safety

The error zone is responsible for dealing with uncaught errors.

This is the closest parent zone of this zone that provides a handleUncaughtError method.

Asynchronous errors never cross zone boundaries between zones with different error handlers.

Example:

import 'dart:async';

main() {
  var future;
  runZoned(() {
    // The asynchronous error is caught by the custom zone which prints
    // 'asynchronous error'.
    future = Future.error("asynchronous error");
  }, onError: (e) { print(e); });  // Creates a zone with an error handler.
  // The following `catchError` handler is never invoked, because the
  // custom zone created by the call to `runZoned` provides an
  // error handler.
  future.catchError((e) { throw "is never reached"; });
}

Note that errors cannot enter a child zone with a different error handler either:

import 'dart:async';

main() {
  runZoned(() {
    // The following asynchronous error is *not* caught by the `catchError`
    // in the nested zone, since errors are not to cross zone boundaries
    // with different error handlers.
    // Instead the error is handled by the current error handler,
    // printing "Caught by outer zone: asynchronous error".
    var future = Future.error("asynchronous error");
    runZoned(() {
      future.catchError((e) { throw "is never reached"; });
    }, onError: (e) { throw "is never reached"; });
  }, onError: (e) { print("Caught by outer zone: $e"); });
}