diff --git a/LibTest/js_interop/NullableUndefineableJSAnyExtension/isDefinedAndNotNull_t01.dart b/LibTest/js_interop/NullableUndefineableJSAnyExtension/isDefinedAndNotNull_t01.dart
new file mode 100644
index 0000000000..26d2297016
--- /dev/null
+++ b/LibTest/js_interop/NullableUndefineableJSAnyExtension/isDefinedAndNotNull_t01.dart
@@ -0,0 +1,28 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// @assertion bool get isDefinedAndNotNull
+///
+/// @description Checks that this getter returns `true` if  this value is
+/// defined (not `undefined`) and not `Null`. `false` otherwise.
+/// @author sgrekhov22@gmail.com
+
+import 'dart:js_interop';
+import 'dart:js_interop_unsafe';
+import '../../../Utils/expect.dart';
+import '../js_utils.dart';
+
+main() {
+  eval(r'''
+    var n = null;
+    var u = undefined;
+    var s = "s";
+  ''');
+
+  Expect.isFalse(globalContext["n"].isDefinedAndNotNull);
+  Expect.isTrue(42.toJS.isDefinedAndNotNull);
+  Expect.isFalse(globalContext["u"].isDefinedAndNotNull);
+  Expect.isTrue(globalContext["s"].isDefinedAndNotNull);
+  Expect.isFalse(null.isDefinedAndNotNull);
+}
diff --git a/LibTest/js_interop/NullableUndefineableJSAnyExtension/isNull_t01.dart b/LibTest/js_interop/NullableUndefineableJSAnyExtension/isNull_t01.dart
new file mode 100644
index 0000000000..ca1e3d9c38
--- /dev/null
+++ b/LibTest/js_interop/NullableUndefineableJSAnyExtension/isNull_t01.dart
@@ -0,0 +1,28 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// @assertion bool get isNull
+/// Whether this value corresponds to JavaScript `null`.
+///
+/// @description Checks if this value corresponds to JavaScript `null`.
+/// @author sgrekhov22@gmail.com
+
+import 'dart:js_interop';
+import 'dart:js_interop_unsafe';
+import '../../../Utils/expect.dart';
+import '../js_utils.dart';
+
+main() {
+  eval(r'''
+    var n = null;
+    var u = undefined;
+    var s = "s";
+  ''');
+
+  Expect.isTrue(globalContext["n"].isNull);
+  Expect.isFalse(42.toJS.isNull);
+  Expect.isFalse(globalContext["u"].isNull);
+  Expect.isFalse(globalContext["s"].isNull);
+  Expect.isTrue(null.isNull);
+}
diff --git a/LibTest/js_interop/NullableUndefineableJSAnyExtension/isUndefinedOrNull_t01.dart b/LibTest/js_interop/NullableUndefineableJSAnyExtension/isUndefinedOrNull_t01.dart
new file mode 100644
index 0000000000..cb43b48bca
--- /dev/null
+++ b/LibTest/js_interop/NullableUndefineableJSAnyExtension/isUndefinedOrNull_t01.dart
@@ -0,0 +1,28 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// @assertion bool get isUndefinedOrNull
+///
+/// @description Checks that this getter returns `true` if the value
+/// corresponds to JavaScript `undefined` or `null`. `false` otherwise.
+/// @author sgrekhov22@gmail.com
+
+import 'dart:js_interop';
+import 'dart:js_interop_unsafe';
+import '../../../Utils/expect.dart';
+import '../js_utils.dart';
+
+main() {
+  eval(r'''
+    var n = null;
+    var u = undefined;
+    var s = "s";
+  ''');
+
+  Expect.isTrue(globalContext["n"].isUndefinedOrNull);
+  Expect.isFalse(42.toJS.isUndefinedOrNull);
+  Expect.isTrue(globalContext["u"].isUndefinedOrNull);
+  Expect.isFalse(globalContext["s"].isUndefinedOrNull);
+  Expect.isTrue(null.isUndefinedOrNull);
+}
diff --git a/LibTest/js_interop/NullableUndefineableJSAnyExtension/isUndefined_t01.dart b/LibTest/js_interop/NullableUndefineableJSAnyExtension/isUndefined_t01.dart
new file mode 100644
index 0000000000..049923375b
--- /dev/null
+++ b/LibTest/js_interop/NullableUndefineableJSAnyExtension/isUndefined_t01.dart
@@ -0,0 +1,28 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// @assertion bool get isUndefined
+/// Whether this value corresponds to JavaScript `undefined`.
+///
+/// @description Checks if this value corresponds to JavaScript `undefined`.
+/// @author sgrekhov22@gmail.com
+
+import 'dart:js_interop';
+import 'dart:js_interop_unsafe';
+import '../../../Utils/expect.dart';
+import '../js_utils.dart';
+
+main() {
+  eval(r'''
+    var n = null;
+    var u = undefined;
+    var s = "s";
+  ''');
+
+  Expect.isFalse(globalContext["n"].isUndefined);
+  Expect.isFalse(42.toJS.isUndefined);
+  Expect.isTrue(globalContext["u"].isUndefined);
+  Expect.isFalse(globalContext["s"].isUndefined);
+  Expect.isFalse(null.isUndefined);
+}
diff --git a/LibTest/js_interop/js_utils.dart b/LibTest/js_interop/js_utils.dart
new file mode 100644
index 0000000000..a25d7ebb02
--- /dev/null
+++ b/LibTest/js_interop/js_utils.dart
@@ -0,0 +1,11 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// @description Common library for js_interop tests.
+/// @author sgrekhov22@gmail.com
+
+import 'dart:js_interop';
+
+@JS()
+external void eval(String code);