#3180. Add JSExport tests. Part 1.

LibTest/js_interop/JSExport/jsExport_A01_t01.dart

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+// 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 Annotation to allow Dart classes to be wrapped with a JS object
+/// using `dart:js_interop`'s `createJSInteropWrapper`.
+///
+/// When an instance of a class annotated with this annotation is passed to
+/// `createJSInteropWrapper`, the method returns a JS object that contains a
+/// property for each of the class' instance members. When called, these
+/// properties forward to the instance's corresponding members.
+///
+/// @description Checks that when an instance of a class annotated with
+/// `@JSExport()` is passed to `createJSInteropWrapper`, the method returns a JS
+/// object that contains a property for each of the class' instance members.
+/// @author sgrekhov22@gmail.com
+
+import 'dart:js_interop';
+import 'dart:js_interop_unsafe';
+import '../../../Utils/expect.dart';
+import '../js_utils.dart';
+
+String log = "";
+
+@JSExport()
+class C {
+  int variable = 42;
+  String method(String v) => "method($v);";
+  String get getter => "Some getter";
+  void set setter(bool value) {
+    log = "setter($value);";
+  }
+}
+
+void main() {
+  var c = C();
+  var jsC = createJSInteropWrapper<C>(c);
+  globalContext["jsC"] = jsC;
+  eval(r'''
+    globalThis.v1 = globalThis.jsC.variable;
+    globalThis.v2 = globalThis.jsC.method('x');
+    globalThis.v3 = globalThis.jsC.getter;
+    globalThis.jsC.setter = false;
+  ''');
+  Expect.equals(42, (globalContext["v1"] as JSNumber).toDartInt);
+  Expect.equals("method(x);", (globalContext["v2"] as JSString).toDart);
+  Expect.equals("Some getter", (globalContext["v3"] as JSString).toDart);
+  Expect.equals("setter(false);", log);
+}

LibTest/js_interop/JSExport/jsExport_A01_t02.dart

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+// 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 Annotation to allow Dart classes to be wrapped with a JS object
+/// using `dart:js_interop`'s `createJSInteropWrapper`.
+///
+/// When an instance of a class annotated with this annotation is passed to
+/// `createJSInteropWrapper`, the method returns a JS object that contains a
+/// property for each of the class' instance members. When called, these
+/// properties forward to the instance's corresponding members.
+///
+/// @description Checks that value of a final variable of a clas annotated with
+/// `@JSExport()` cannot be changed.
+/// @author sgrekhov22@gmail.com
+
+import 'dart:js_interop';
+import 'dart:js_interop_unsafe';
+import '../../../Utils/expect.dart';
+import '../js_utils.dart';
+
+@JSExport()
+class C {
+  final int variable = 42;
+}
+
+void main() {
+  var c = C();
+  var jsC = createJSInteropWrapper<C>(c);
+  globalContext["jsC"] = jsC;
+  eval(r'''
+    globalThis.jsC.variable = 0;
+    globalThis.v = globalThis.jsC.variable;
+  ''');
+  Expect.equals(42, (globalContext["v"] as JSNumber).toDartInt);
+}

LibTest/js_interop/JSExport/jsExport_A01_t03.dart

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+// 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 Annotation to allow Dart classes to be wrapped with a JS object
+/// using `dart:js_interop`'s `createJSInteropWrapper`.
+///
+/// When an instance of a class annotated with this annotation is passed to
+/// `createJSInteropWrapper`, the method returns a JS object that contains a
+/// property for each of the class' instance members. When called, these
+/// properties forward to the instance's corresponding members.
+///
+/// @description Checks that uninitialized late instance variables of a class
+/// annotated with `@JSExport()` are created by `createJSInteropWrapper` and
+/// produce a runtime error when read before initialization.
+/// @author sgrekhov22@gmail.com
+
+import 'dart:js_interop';
+import 'dart:js_interop_unsafe';
+import '../../../Utils/expect.dart';
+import '../js_utils.dart';
+
+@JSExport()
+class C {
+  late int variable;
+
+  void init() {
+    variable = 42;
+  }
+}
+
+void main() {
+  var c = C();
+  var jsC = createJSInteropWrapper<C>(c);
+  globalContext["jsC"] = jsC;
+  Expect.throws(() {
+    eval("globalThis.jsC.variable;"); // LateInitializationError
+  });
+
+  c.init();
+  eval("globalThis.v1 = globalThis.jsC.variable;");
+  Expect.equals(42, (globalContext["v1"] as JSNumber).toDartInt);
+}

LibTest/js_interop/JSExport/jsExport_A01_t04.dart

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+// 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 Annotation to allow Dart classes to be wrapped with a JS object
+/// using `dart:js_interop`'s `createJSInteropWrapper`.
+///
+/// When an instance of a class annotated with this annotation is passed to
+/// `createJSInteropWrapper`, the method returns a JS object that contains a
+/// property for each of the class' instance members. When called, these
+/// properties forward to the instance's corresponding members.
+///
+/// @description Checks that it is a compile-time error if a class or a mixin
+/// annotated with `@JSExport()` doesn't contain any instance members.
+/// @author sgrekhov22@gmail.com
+
+import 'dart:js_interop';
+
+@JSExport()
+class C1 {
+//    ^^
+// [analyzer] unspecified
+// [web] unspecified
+  static int variable = 42;
+  static String method(String v) => "method($v);";
+  static String get getter => "Some getter";
+  static void set setter(bool value) {}
+}
+
+@JSExport()
+class C2 {
+//    ^^
+// [analyzer] unspecified
+// [web] unspecified
+  C2();
+  C2.x();
+  factory C2.f() = C2.x;
+}
+
+@JSExport()
+mixin M {
+//    ^
+// [analyzer] unspecified
+// [web] unspecified
+  static int variable = 42;
+  static String method(String v) => "method($v);";
+  static String get getter => "Some getter";
+  static void set setter(bool value) {}
+}
+
+void main() {
+  print(C1);
+  print(C2);
+  print(M);
+}

LibTest/js_interop/JSExport/jsExport_A01_t05.dart

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+// 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 Annotation to allow Dart classes to be wrapped with a JS object
+/// using `dart:js_interop`'s `createJSInteropWrapper`.
+///
+/// When an instance of a class annotated with this annotation is passed to
+/// `createJSInteropWrapper`, the method returns a JS object that contains a
+/// property for each of the class' instance members. When called, these
+/// properties forward to the instance's corresponding members.
+///
+/// @description Checks that when an instance of a class annotated with
+/// `@JSExport()` is passed to `createJSInteropWrapper`, the method returns a JS
+/// object that contains a property for each of the class' instance members.
+/// Test type variables.
+/// @author sgrekhov22@gmail.com
+
+import 'dart:js_interop';
+import 'dart:js_interop_unsafe';
+import '../../../Utils/expect.dart';
+import '../js_utils.dart';
+
+String log = "";
+
+@JSExport()
+class C<X, Y> {
+  X variable;
+  X method(Y y) {
+    log = "method($y) => $variable;";
+    return variable;
+  }
+  X get getter => variable;
+  void set setter(Y y) {
+    log = "setter($y);";
+  }
+  C(this.variable);
+}
+
+void main() {
+  var c = C<int, String>(42);
+  var jsC = createJSInteropWrapper<C<int, String>>(c);
+  globalContext["jsC"] = jsC;
+  eval(r'''
+    globalThis.v1 = globalThis.jsC.variable;
+    globalThis.v2 = globalThis.jsC.method('x');
+    globalThis.v3 = globalThis.jsC.getter;
+  ''');
+  Expect.equals(42, (globalContext["v1"] as JSNumber).toDartInt);
+  Expect.equals("method(x) => 42;", log);
+  Expect.equals(42, (globalContext["v3"] as JSNumber).toDartInt);
+
+  eval("globalThis.jsC.setter = 'z';");
+  Expect.equals("setter(z);", log);
+}