tests/lib_2/js/js_util/promise_reject_null_test.dart

// @dart = 2.9
@JS()
library promise_reject_null_test;

import 'package:js/js.dart';
import 'package:js/js_util.dart' show promiseToFuture, NullRejectionException;

import 'package:expect/minitest.dart';

@JS()
external void eval(String s);

@JS('Promise.reject')
external dynamic getRejectedPromise(v);

@JS()
external void reject(v);
@JS()
external dynamic getNewPromise();

void main() async {
  eval('''
    self.getNewPromise = function () {
      return new Promise(function (_, reject) {
        self.reject = reject;
      });
    };
  ''');

  // Rejected promise with a `null` value should trigger a
  // `NullRejectionException`.
  await promiseToFuture(getRejectedPromise(null)).then((_) {
    fail("Expected promise to reject and not fulfill.");
  }).catchError((e) {
    expect(e is NullRejectionException, true);
    expect(e.isUndefined, false);
  });

  // Similar to the above, except we reject using JS interop.
  var future = promiseToFuture(getNewPromise()).then((_) {
    fail("Expected promise to reject and not fulfill.");
  }).catchError((e) {
    expect(e is NullRejectionException, true);
    expect(e.isUndefined, false);
  });

  reject(null);

  await future;

  // It's also possible to reject with `undefined`. Make sure that the exception
  // correctly flags that case.
  future = promiseToFuture(getNewPromise()).then((_) {
    fail("Expected promise to reject and not fulfill.");
  }).catchError((e) {
    expect(e is NullRejectionException, true);
    expect(e.isUndefined, true);
  });

  eval('''
    self.reject(undefined);
  ''');

  await future;
}