diff --git a/LibTest/js_interop/anonymous_A01_t01.dart b/LibTest/js_interop/anonymous_A01_t01.dart
new file mode 100644
index 0000000000..556619c82d
--- /dev/null
+++ b/LibTest/js_interop/anonymous_A01_t01.dart
@@ -0,0 +1,41 @@
+// 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 An annotation that indicates a JS annotated class is structural
+/// and does not have a known JavaScript prototype.
+///
+/// A class marked with [anonymous] must have an unnamed factory constructor
+/// with no positional arguments, only named arguments. Invoking the constructor
+/// desugars to creating a JavaScript object literal with name-value pairs
+/// corresponding to the parameter names and values.
+///
+/// @description Checks that invoking the constructor desugars to creating a
+/// JavaScript object literal with name-value pairs corresponding to the
+/// parameter names and values.
+/// @author sgrekhov22@gmail.com
+
+import 'dart:js_interop';
+import 'dart:js_interop_unsafe';
+import '../../Utils/expect.dart';
+import 'js_utils.dart';
+
+@anonymous
+@staticInterop
+@JS()
+class C {
+  external factory C({String s, int n, bool b});
+}
+
+main() {
+  var c = C(s: "s value", n: 42, b: true);
+  globalContext["c"] = c as JSObject;
+  eval(r'''
+    globalThis.resS = globalThis.c.s;
+    globalThis.resN = globalThis.c.n;
+    globalThis.resB = globalThis.c.b;
+  ''');
+  Expect.equals("s value", (globalContext["resS"] as JSString).toDart);
+  Expect.equals(42, (globalContext["resN"] as JSNumber).toDartInt);
+  Expect.equals(true, (globalContext["resB"] as JSBoolean).toDart);
+}
diff --git a/LibTest/js_interop/anonymous_A01_t02.dart b/LibTest/js_interop/anonymous_A01_t02.dart
new file mode 100644
index 0000000000..bbdcdd40ff
--- /dev/null
+++ b/LibTest/js_interop/anonymous_A01_t02.dart
@@ -0,0 +1,41 @@
+// 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 An annotation that indicates a JS annotated class is structural
+/// and does not have a known JavaScript prototype.
+///
+/// A class marked with [anonymous] must have an unnamed factory constructor
+/// with no positional arguments, only named arguments. Invoking the constructor
+/// desugars to creating a JavaScript object literal with name-value pairs
+/// corresponding to the parameter names and values.
+///
+/// @description Checks that invoking the constructor desugars to creating a
+/// JavaScript object literal with name-value pairs corresponding to the
+/// parameter names and values. Test a named factory constructor.
+/// @author sgrekhov22@gmail.com
+
+import 'dart:js_interop';
+import 'dart:js_interop_unsafe';
+import '../../Utils/expect.dart';
+import 'js_utils.dart';
+
+@anonymous
+@staticInterop
+@JS()
+class C {
+  external factory C.f({String s, int n, bool b});
+}
+
+main() {
+  var c = C.f(s: "s value", n: 42, b: true);
+  globalContext["c"] = c as JSObject;
+  eval(r'''
+    globalThis.resS = globalThis.c.s;
+    globalThis.resN = globalThis.c.n;
+    globalThis.resB = globalThis.c.b;
+  ''');
+  Expect.equals("s value", (globalContext["resS"] as JSString).toDart);
+  Expect.equals(42, (globalContext["resN"] as JSNumber).toDartInt);
+  Expect.equals(true, (globalContext["resB"] as JSBoolean).toDart);
+}
diff --git a/LibTest/js_interop/anonymous_A02_t01.dart b/LibTest/js_interop/anonymous_A02_t01.dart
new file mode 100644
index 0000000000..8da886e7f2
--- /dev/null
+++ b/LibTest/js_interop/anonymous_A02_t01.dart
@@ -0,0 +1,39 @@
+// 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 An annotation that indicates a JS annotated class is structural
+/// and does not have a known JavaScript prototype.
+///
+/// A class marked with [anonymous] must have an unnamed factory constructor
+/// with no positional arguments, only named arguments. Invoking the constructor
+/// desugars to creating a JavaScript object literal with name-value pairs
+/// corresponding to the parameter names and values.
+///
+/// @description Checks that it is not an error if a class annotated with
+/// [anonymous] has no unnamed factory constructor. Creating an instance creates
+/// an empty JS object.
+/// @author sgrekhov22@gmail.com
+
+import 'dart:js_interop';
+import 'dart:js_interop_unsafe';
+import 'js_utils.dart';
+
+@anonymous
+class C1 {
+}
+
+@anonymous
+@staticInterop
+@JS()
+abstract class C2 {
+}
+
+main() {
+  globalContext["o"] = C1().jsify();
+  eval(r'''
+    globalThis.keys = Object.keys(globalThis.o);
+  ''');
+  jsExpectArrayEquals(JSArray(), globalContext["keys"]);
+  print(C2);
+}
diff --git a/LibTest/js_interop/anonymous_A03_t01.dart b/LibTest/js_interop/anonymous_A03_t01.dart
new file mode 100644
index 0000000000..761e83fde1
--- /dev/null
+++ b/LibTest/js_interop/anonymous_A03_t01.dart
@@ -0,0 +1,69 @@
+// 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 An annotation that indicates a JS annotated class is structural
+/// and does not have a known JavaScript prototype.
+///
+/// A class marked with [anonymous] must have an unnamed factory constructor
+/// with no positional arguments, only named arguments. Invoking the constructor
+/// desugars to creating a JavaScript object literal with name-value pairs
+/// corresponding to the parameter names and values.
+///
+/// @description Checks that it is a warning if an extension type is annotated
+/// with [anonymous].
+/// @author sgrekhov22@gmail.com
+/// @issue 61018
+
+import 'dart:js_interop';
+
+@anonymous
+@JS()
+extension type Ext1(JSObject _) {
+//             ^^^^
+// [analyzer] unspecified
+// [web] unspecified
+}
+
+@anonymous
+@JS()
+extension type Ext2.x(JSObject _) {
+//             ^^^^
+// [analyzer] unspecified
+// [web] unspecified
+
+  external factory Ext2({String id});
+}
+
+@anonymous
+@staticInterop
+@JS()
+extension type Ext3._(JSObject _) {
+//             ^^^^
+// [analyzer] unspecified
+// [web] unspecified
+  external factory Ext3({String id});
+}
+
+@anonymous
+extension type Ext4(JSObject id) {
+//             ^^^^
+// [analyzer] unspecified
+// [web] unspecified
+}
+
+@anonymous
+extension type Ext5.x(JSObject id) {
+//             ^^^^
+// [analyzer] unspecified
+// [web] unspecified
+  factory Ext5(JSObject id) = Ext5.x;
+}
+
+main() {
+  print(Ext1);
+  print(Ext2);
+  print(Ext3);
+  print(Ext4);
+  print(Ext5);
+}
diff --git a/LibTest/js_interop/anonymous_A03_t02.dart b/LibTest/js_interop/anonymous_A03_t02.dart
new file mode 100644
index 0000000000..9f9a94bd21
--- /dev/null
+++ b/LibTest/js_interop/anonymous_A03_t02.dart
@@ -0,0 +1,51 @@
+// 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 An annotation that indicates a JS annotated class is structural
+/// and does not have a known JavaScript prototype.
+///
+/// A class marked with [anonymous] must have an unnamed factory constructor
+/// with no positional arguments, only named arguments. Invoking the constructor
+/// desugars to creating a JavaScript object literal with name-value pairs
+/// corresponding to the parameter names and values.
+///
+/// @description Checks that it is a compile-time error if an enum is annotated
+/// with [anonymous].
+/// @author sgrekhov22@gmail.com
+/// @issue 61115
+
+import 'dart:js_interop';
+
+@anonymous
+@staticInterop
+@JS()
+enum E1 {
+//   ^^
+// [analyzer] unspecified
+// [web] unspecified
+  e0;
+}
+
+@anonymous
+@JS()
+enum E2 {
+//   ^^
+// [analyzer] unspecified
+// [web] unspecified
+  e0;
+}
+
+@anonymous
+enum E3 {
+//   ^^
+// [analyzer] unspecified
+// [web] unspecified
+  e0;
+}
+
+main() {
+  print(E1);
+  print(E2);
+  print(E3);
+}
diff --git a/LibTest/js_interop/anonymous_A03_t03.dart b/LibTest/js_interop/anonymous_A03_t03.dart
new file mode 100644
index 0000000000..decf4cfd4c
--- /dev/null
+++ b/LibTest/js_interop/anonymous_A03_t03.dart
@@ -0,0 +1,48 @@
+// 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 An annotation that indicates a JS annotated class is structural
+/// and does not have a known JavaScript prototype.
+///
+/// A class marked with [anonymous] must have an unnamed factory constructor
+/// with no positional arguments, only named arguments. Invoking the constructor
+/// desugars to creating a JavaScript object literal with name-value pairs
+/// corresponding to the parameter names and values.
+///
+/// @description Checks that it is a compile-time error if a mixin is annotated
+/// with [anonymous].
+/// @author sgrekhov22@gmail.com
+/// @issue 61018
+
+import 'dart:js_interop';
+
+@anonymous
+@JS()
+mixin M1 {
+//    ^^
+// [analyzer] unspecified
+// [web] unspecified
+}
+
+@anonymous
+@staticInterop
+@JS()
+mixin M2 {
+//    ^^
+// [analyzer] unspecified
+// [web] unspecified
+}
+
+@anonymous
+mixin M3 {
+//    ^^
+// [analyzer] unspecified
+// [web] unspecified
+}
+
+main() {
+  print(M1);
+  print(M2);
+  print(M3);
+}
diff --git a/LibTest/js_interop/anonymous_A03_t04.dart b/LibTest/js_interop/anonymous_A03_t04.dart
new file mode 100644
index 0000000000..55ced9f92f
--- /dev/null
+++ b/LibTest/js_interop/anonymous_A03_t04.dart
@@ -0,0 +1,49 @@
+// 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 An annotation that indicates a JS annotated class is structural
+/// and does not have a known JavaScript prototype.
+///
+/// A class marked with [anonymous] must have an unnamed factory constructor
+/// with no positional arguments, only named arguments. Invoking the constructor
+/// desugars to creating a JavaScript object literal with name-value pairs
+/// corresponding to the parameter names and values.
+///
+/// @description Checks that it is a compile-time error if an extension
+/// is annotated with `@anonymous`.
+/// @author sgrekhov22@gmail.com
+
+import 'dart:js_interop';
+
+class C1 {
+  C1.n({String id = ""});
+  factory C1({String id}) = C1.n;
+}
+
+@anonymous
+@JS()
+extension Ext1 on C1 {
+//        ^^^^
+// [analyzer] unspecified
+// [web] unspecified
+}
+
+@anonymous
+@staticInterop
+@JS()
+class C2 {
+  external factory C2({String id});
+}
+
+@anonymous
+extension Ext2 on C2 {
+//        ^^^^
+// [analyzer] unspecified
+// [web] unspecified
+}
+
+main() {
+   print(C1);
+   print(C2);
+}
diff --git a/LibTest/js_interop/anonymous_A03_t05.dart b/LibTest/js_interop/anonymous_A03_t05.dart
new file mode 100644
index 0000000000..9d54ecb27e
--- /dev/null
+++ b/LibTest/js_interop/anonymous_A03_t05.dart
@@ -0,0 +1,50 @@
+// 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 An annotation that indicates a JS annotated class is structural
+/// and does not have a known JavaScript prototype.
+///
+/// A class marked with [anonymous] must have an unnamed factory constructor
+/// with no positional arguments, only named arguments. Invoking the constructor
+/// desugars to creating a JavaScript object literal with name-value pairs
+/// corresponding to the parameter names and values.
+///
+/// @description Checks that it is a compile-time error if a non-type is marked
+/// with [anonymous].
+/// @author sgrekhov22@gmail.com
+/// @issue 61109
+
+import 'dart:js_interop';
+
+@anonymous
+void foo() {}
+//   ^^^
+// [analyzer] unspecified
+// [web] unspecified
+
+@anonymous
+@JS()
+int get bar => 42;
+//      ^^^
+// [analyzer] unspecified
+// [web] unspecified
+
+@anonymous
+@JS()
+String baz = "baz";
+//     ^^^
+// [analyzer] unspecified
+// [web] unspecified
+
+@anonymous
+void set qux(int _) {}
+//       ^^^
+// [analyzer] unspecified
+// [web] unspecified
+
+main() {
+   print(foo);
+   print(bar);
+   print(baz);
+}