diff --git a/LibTest/js_interop/JS/js_A03_t01.dart b/LibTest/js_interop/JS/js_A03_t01.dart
new file mode 100644
index 0000000000..f46174db84
--- /dev/null
+++ b/LibTest/js_interop/JS/js_A03_t01.dart
@@ -0,0 +1,71 @@
+// 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 on a JavaScript interop declaration.
+/// ...
+/// Specifying name customizes the JavaScript name to use, which can be used in
+/// the following scenarios:
+/// - Adding a JavaScript prefix to all the external top-level declarations,
+///   static members, and constructors of a library by parameterizing the
+///   annotation on the library with `name`.
+/// - Specifying the JavaScript class to use for external static members and
+///   constructors of an interop extension type by parameterizing the annotation
+///   on the interop extension type with `name`.
+/// - Renaming external declarations by parameterizing the annotation on the
+///   member with `name`.
+///
+/// @description Check that specifying `name` customizes the JavaScript `name`
+/// to use. Test top-level declarations.
+/// @author sgrekhov22@gmail.com
+
+import 'dart:js_interop';
+import 'dart:js_interop_unsafe';
+import '../../../Utils/expect.dart';
+import '../js_utils.dart';
+
+@JS("jsVar1")
+external int var1;
+
+@JS("jsVar2")
+external final String var2;
+
+@JS("jsGetter")
+external int get getter;
+
+@JS("jsF1")
+external int f1();
+
+@JS("jsF2")
+external int f2(int v);
+
+@JS("jsSetter")
+external void set setter(int v);
+
+main() {
+  eval(r'''
+    globalThis.jsVar1 = 42; 
+    globalThis.jsVar2 = "var2 value";
+    globalThis.jsGetter = -1;
+    globalThis.jsF1 = function() {return 1;};
+    globalThis.jsF2 = function(v) {return v;};
+    globalThis.jsSetter = 0;
+    
+    globalThis.var1 = -42; 
+    globalThis.var2 = "Wrong var2 value";
+    globalThis.getter = -100;
+    globalThis.f1 = function() {return 100;};
+    globalThis.f2 = function(v) {return 100 + v;};
+    globalThis.setter = 100;
+  ''');
+  Expect.equals(42, var1);
+  Expect.equals("var2 value", var2);
+  Expect.equals(-1, getter);
+  Expect.equals(1, f1());
+  Expect.equals(2, f2(2));
+  setter = 3;
+  Expect.equals(3, (globalContext["jsSetter"] as JSNumber).toDartInt);
+  var1 = -1;
+  eval("globalThis.jsVar1++");
+  Expect.equals(0, var1);
+}
diff --git a/LibTest/js_interop/JS/js_A03_t02.dart b/LibTest/js_interop/JS/js_A03_t02.dart
new file mode 100644
index 0000000000..689d995c3d
--- /dev/null
+++ b/LibTest/js_interop/JS/js_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 on a JavaScript interop declaration.
+/// ...
+/// Specifying name customizes the JavaScript name to use, which can be used in
+/// the following scenarios:
+/// - Adding a JavaScript prefix to all the external top-level declarations,
+///   static members, and constructors of a library by parameterizing the
+///   annotation on the library with `name`.
+/// - Specifying the JavaScript class to use for external static members and
+///   constructors of an interop extension type by parameterizing the annotation
+///   on the interop extension type with `name`.
+/// - Renaming external declarations by parameterizing the annotation on the
+///   member with `name`.
+///
+/// @description Check that specifying `name` customizes the JavaScript `name`
+/// to use. Test extension type declaration.
+/// @author sgrekhov22@gmail.com
+
+import 'dart:js_interop';
+import 'dart:js_interop_unsafe';
+import '../../../Utils/expect.dart';
+import '../js_utils.dart';
+
+@JS("JSEt")
+extension type ET(JSObject _) implements JSObject {
+  external String foo();
+  external static String bar();
+}
+
+main() {
+  eval(r'''
+    class JSEt {
+      foo() {
+        return "foo() from JSEt";
+      }
+      
+      static bar() {
+        return "bar() from JSEt";
+      }
+    }
+    globalThis.JSEt = JSEt;
+    globalThis.et = new JSEt();
+  ''');
+
+  ET et = ET(globalContext["et"] as JSObject);
+  Expect.equals("foo() from JSEt", et.foo());
+  Expect.equals("bar() from JSEt", ET.bar());
+}
diff --git a/LibTest/js_interop/JS/js_A03_t03.dart b/LibTest/js_interop/JS/js_A03_t03.dart
new file mode 100644
index 0000000000..6e4c273ccc
--- /dev/null
+++ b/LibTest/js_interop/JS/js_A03_t03.dart
@@ -0,0 +1,83 @@
+// 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 on a JavaScript interop declaration.
+/// ...
+/// Specifying name customizes the JavaScript name to use, which can be used in
+/// the following scenarios:
+/// - Adding a JavaScript prefix to all the external top-level declarations,
+///   static members, and constructors of a library by parameterizing the
+///   annotation on the library with `name`.
+/// - Specifying the JavaScript class to use for external static members and
+///   constructors of an interop extension type by parameterizing the annotation
+///   on the interop extension type with `name`.
+/// - Renaming external declarations by parameterizing the annotation on the
+///   member with `name`.
+///
+/// @description Check that specifying `name` customizes the JavaScript `name`
+/// to use. Test members of an extension type.
+/// @author sgrekhov22@gmail.com
+
+import 'dart:js_interop';
+import 'dart:js_interop_unsafe';
+import '../../../Utils/expect.dart';
+import '../js_utils.dart';
+
+extension type ET(JSObject _) implements JSObject {
+  @JS("jsVar1")
+  external int var1;
+
+  @JS("jsVar2")
+  external final String var2;
+
+  @JS("jsX")
+  external int get x;
+
+  @JS("jsX")
+  external void set x(int v);
+
+  @JS("jsF1")
+  external int f1();
+
+  @JS("jsF2")
+  external int f2(int v);
+}
+
+main() {
+  eval(r'''
+    class ET {
+      constructor(v1, v2) {
+        this.jsVar1 = v1;
+        this.jsVar2 = v2;
+        this._x = 0;
+      }
+      
+      get jsX() {
+        return this._x;
+      }
+      
+      set jsX(v) {
+        this._x = v;
+      }
+      
+      jsF1() {
+        return this.jsVar1;
+      }
+      
+      jsF2(v) {
+        return v;
+      }
+    }
+    globalThis.et = new ET(1, "two");
+  ''');
+
+  ET et = ET(globalContext["et"] as JSObject);
+  Expect.equals(1, et.var1);
+  Expect.equals("two", et.var2);
+  Expect.equals(0, et.x);
+  Expect.equals(1, et.f1());
+  Expect.equals(2, et.f2(2));
+  et.x = 3;
+  Expect.equals(3, et.x);
+}
diff --git a/LibTest/js_interop/JS/js_A03_t04.dart b/LibTest/js_interop/JS/js_A03_t04.dart
new file mode 100644
index 0000000000..e36a4c9a75
--- /dev/null
+++ b/LibTest/js_interop/JS/js_A03_t04.dart
@@ -0,0 +1,79 @@
+// 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 on a JavaScript interop declaration.
+/// ...
+/// Specifying name customizes the JavaScript name to use, which can be used in
+/// the following scenarios:
+/// - Adding a JavaScript prefix to all the external top-level declarations,
+///   static members, and constructors of a library by parameterizing the
+///   annotation on the library with `name`.
+/// - Specifying the JavaScript class to use for external static members and
+///   constructors of an interop extension type by parameterizing the annotation
+///   on the interop extension type with `name`.
+/// - Renaming external declarations by parameterizing the annotation on the
+///   member with `name`.
+///
+/// @description Check that specifying `name` customizes the JavaScript `name`
+/// to use. Test static members of an extension type.
+/// @author sgrekhov22@gmail.com
+
+import 'dart:js_interop';
+import 'dart:js_interop_unsafe';
+import '../../../Utils/expect.dart';
+import '../js_utils.dart';
+
+extension type ET(JSObject _) implements JSObject {
+  @JS("jsVar1")
+  external static int var1;
+
+  @JS("jsVar2")
+  external static final String var2;
+
+  @JS("jsX")
+  external static int get x;
+
+  @JS("jsX")
+  external static void set x(int v);
+
+  @JS("jsF1")
+  external static int f1();
+
+  @JS("jsF2")
+  external static int f2(int v);
+}
+
+main() {
+  eval(r'''
+    class ET {
+      static jsVar1 = 1;
+      static jsVar2 = "two";
+      static _x = 0;
+      
+      static get jsX() {
+        return ET._x;
+      }
+      
+      static set jsX(v) {
+        ET._x = v;
+      }
+      
+      static jsF1() {
+        return ET.jsVar1;
+      }
+      
+      static jsF2(v) {
+        return v;
+      }
+    }
+    globalThis.ET = ET;
+  ''');
+  Expect.equals(1, ET.var1);
+  Expect.equals("two", ET.var2);
+  Expect.equals(0, ET.x);
+  Expect.equals(1, ET.f1());
+  Expect.equals(2, ET.f2(2));
+  ET.x = 3;
+  Expect.equals(3, ET.x);
+}
diff --git a/LibTest/js_interop/JS/js_A03_t05.dart b/LibTest/js_interop/JS/js_A03_t05.dart
new file mode 100644
index 0000000000..0d62367a71
--- /dev/null
+++ b/LibTest/js_interop/JS/js_A03_t05.dart
@@ -0,0 +1,47 @@
+// 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 on a JavaScript interop declaration.
+///
+/// This annotation defines a given library, top-level external declaration, or
+/// extension type as a JavaScript interop declaration.
+///
+/// @description Check that a library directive can be annotated with a `@JS()`
+/// annotation.
+/// @author sgrekhov22@gmail.com
+
+@JS("lib1")
+library;
+
+import 'dart:async';
+import 'dart:js_interop';
+import 'dart:js_interop_unsafe';
+import '../../../Utils/expect.dart';
+import '../js_utils.dart';
+
+@JS()
+external int answer();
+
+final completer = Completer<String>();
+
+void complete(String value) {
+  completer.complete(value);
+}
+
+main() {
+  globalContext["complete"] = complete.toJS;
+  eval(r'''
+    var lib1;
+    (async () => { 
+      lib1 = await import('/root_dart/tests/co19/src/LibTest/js_interop/module.js');
+    })().then(function(v) {
+      globalThis.complete("");
+    });
+  ''');
+  asyncStart();
+  completer.future.then((_) {
+    Expect.equals(42, answer()); // calls lib1.answer()
+    asyncEnd();
+  });
+}
diff --git a/LibTest/js_interop/JSAnyUtilityExtension/instanceOfString_A04_t01.dart b/LibTest/js_interop/JSAnyUtilityExtension/instanceOfString_A04_t01.dart
index a274ddd93c..8786c6adfd 100644
--- a/LibTest/js_interop/JSAnyUtilityExtension/instanceOfString_A04_t01.dart
+++ b/LibTest/js_interop/JSAnyUtilityExtension/instanceOfString_A04_t01.dart
@@ -20,7 +20,6 @@
 /// `constructorName`. Test the case when `constructorName` contains '.'.
 /// @author sgrekhov22@gmail.com
 
-// OtherResources=module.js
 import 'dart:async';
 import 'dart:js_interop';
 import 'dart:js_interop_unsafe';
@@ -39,7 +38,7 @@ main() {
     var lib1;
     (async () => { 
       // This is path to the module on tryjobs. May not work locally.
-      lib1 = await import('/root_dart/tests/co19/src/LibTest/js_interop/JSAnyUtilityExtension/module.js');
+      lib1 = await import('/root_dart/tests/co19/src/LibTest/js_interop/module.js');
       globalThis.objA = new lib1.A(42, "A form JS");
       globalThis.objB = new lib1.B();
     })().then(function(v) {
diff --git a/LibTest/js_interop/JSAnyUtilityExtension/instanceOfString_A04_t02.dart b/LibTest/js_interop/JSAnyUtilityExtension/instanceOfString_A04_t02.dart
index 4285d869ec..78d5200afe 100644
--- a/LibTest/js_interop/JSAnyUtilityExtension/instanceOfString_A04_t02.dart
+++ b/LibTest/js_interop/JSAnyUtilityExtension/instanceOfString_A04_t02.dart
@@ -20,7 +20,6 @@
 /// `constructorName`. Test the case when `constructorName` contains '.'.
 /// @author sgrekhov22@gmail.com
 
-// OtherResources=module.js
 import 'dart:async';
 import 'dart:js_interop';
 import 'dart:js_interop_unsafe';
@@ -48,7 +47,7 @@ main() {
     var lib1;
     (async () => { 
       // This is path to the module on tryjobs. May not work locally.
-      lib1 = await import('/root_dart/tests/co19/src/LibTest/js_interop/JSAnyUtilityExtension/module.js');
+      lib1 = await import('/root_dart/tests/co19/src/LibTest/js_interop/module.js');
       globalThis.objA = new lib1.A(42, "A form JS");
       globalThis.objB = new lib1.B();
     })().then(function(v) {
diff --git a/LibTest/js_interop/JSAnyUtilityExtension/module.js b/LibTest/js_interop/module.js
similarity index 68%
rename from LibTest/js_interop/JSAnyUtilityExtension/module.js
rename to LibTest/js_interop/module.js
index 8488df28e2..9629b6097d 100644
--- a/LibTest/js_interop/JSAnyUtilityExtension/module.js
+++ b/LibTest/js_interop/module.js
@@ -4,3 +4,7 @@ export function A(id, name) {
 }
 
 export function B() {}
+
+export function answer() {
+  return 42;
+}