[dart:js_interop] Make isA<JSExportedDartFunction>() check that it's a wrapped function

Closes https://github.com/dart-lang/sdk/issues/62573

isA<JSExportedDartFunction>() used to just check if the object
was a function, leading to a possible runtime error if `toDart`
is called. Fixes that by introducing some helpers and moving
around some functions in the JS compilers to other internal
libraries (public members can't be added to
js_allow_interop_patch.dart). Also fixes a minor issue in dart2js
where `allowInterop`ed functions could successfully invoke
`JSExportedDartFunction.toDart`.

CoreLibraryReviewExempt: Documentation change.
Change-Id: I5a9d7c31d3143eb3fb6ebd3273a4bf06ca329479
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/482967
Reviewed-by: Martin Kustermann <kustermann@google.com>
Commit-Queue: Srujan Gaddam <srujzs@google.com>
Reviewed-by: Nate Biggs <natebiggs@google.com>

CHANGELOG.md

@@ -79,6 +79,14 @@ main() {
   functions must now also accept an `instantiator` callback to which they
   should pass the loaded results.
 
+#### dart2js
+
+- `JSExportedDartFunction.toDart` sometimes incorrectly returned the original
+  Dart function even if the wrapper JS function was cast from a call to the
+  deprecated `allowInterop`. Instead, to be consistent with DDC and dart2wasm,
+  it now throws if the wrapper JS function wasn't a result of `Function.toJS` or
+  `Function.toJSCaptureThis`.
+
 ### Libraries
 
 #### `dart:js_interop`
@@ -92,6 +100,9 @@ main() {
   the supertype `Object?`, this change is only breaking if users referred to the
   extension name directly, either through applying the extension directly or
   through using `show`/`hide` directives.
+- `isA<JSExportedDartFunction>()` now checks if the function is actually a JS
+  wrapper function that is returned from `Function.toJS` or
+  `Function.toJSCaptureThis`.
 
 [#56905]: https://github.com/dart-lang/sdk/issues/56905
 

pkg/_js_interop_checks/lib/src/transformations/shared_interop_transformer.dart

@@ -36,9 +36,11 @@ class SharedInteropTransformer extends Transformer {
   final Procedure _isATearoff;
   final Procedure _isJSAny;
   final Procedure _isJSBoxedDartObject;
+  final Procedure _isJSExportedDartFunction;
   final Procedure _isJSObject;
   final Procedure _isNullableJSAny;
   final Procedure _isNullableJSBoxedDartObject;
+  final Procedure _isNullableJSExportedDartFunction;
   final Procedure _isNullableJSObject;
   final ExtensionTypeDeclaration _jsAny;
   final ExtensionTypeDeclaration _jsFunction;
@@ -103,6 +105,8 @@ class SharedInteropTransformer extends Transformer {
       ),
       _isJSBoxedDartObject = _typeEnvironment.coreTypes.index
           .getTopLevelProcedure('dart:js_interop', '_isJSBoxedDartObject'),
+      _isJSExportedDartFunction = _typeEnvironment.coreTypes.index
+          .getTopLevelProcedure('dart:js_interop', '_isJSExportedDartFunction'),
       _isJSObject = _typeEnvironment.coreTypes.index.getTopLevelProcedure(
         'dart:js_interop',
         '_isJSObject',
@@ -116,6 +120,11 @@ class SharedInteropTransformer extends Transformer {
             'dart:js_interop',
             '_isNullableJSBoxedDartObject',
           ),
+      _isNullableJSExportedDartFunction = _typeEnvironment.coreTypes.index
+          .getTopLevelProcedure(
+            'dart:js_interop',
+            '_isNullableJSExportedDartFunction',
+          ),
       _isNullableJSObject = _typeEnvironment.coreTypes.index
           .getTopLevelProcedure('dart:js_interop', '_isNullableJSObject'),
       _jsAny = _typeEnvironment.coreTypes.index.getExtensionType(
@@ -601,8 +610,6 @@ class SharedInteropTransformer extends Transformer {
     Expression? check;
     String? typeofString;
     String? instanceOfString;
-    // TODO(srujzs): Add specific check for `JSExportedDartFunction`.
-    // https://github.com/dart-lang/sdk/issues/62573
     // TODO(srujzs): Maybe use `Array.isArray` for `JSArray`.
     // https://github.com/dart-lang/sdk/issues/62699
     switch (jsTypeName) {
@@ -643,6 +650,18 @@ class SharedInteropTransformer extends Transformer {
           Arguments([VariableGet(receiverVar)]),
         );
         break;
+      case 'JSExportedDartFunction' when interopTypeDecl == jsType:
+        // Only do this special case when users are referring directly to the
+        // `dart:js_interop` type and not some wrapper.
+        isJSAnyCheck = null;
+        nullChecksNeeded = false;
+        check = StaticInvocation(
+          interopTypeNullable
+              ? _isNullableJSExportedDartFunction
+              : _isJSExportedDartFunction,
+          Arguments([VariableGet(receiverVar)]),
+        );
+        break;
       case 'JSTypedArray' when interopTypeDecl == jsType:
         // Only do this special case when users are referring directly to the
         // `dart:js_interop` type and not some wrapper.

pkg/dart2wasm/lib/js/callback_specializer.dart

@@ -200,12 +200,12 @@ class CallbackSpecializer {
   /// Create a [Procedure] that will wrap a Dart callback in a JS wrapper.
   ///
   /// [node] is the conversion function that is called by the user (either
-  /// `allowInterop`, `Function.toJS`, or `Function.toJSCaptureThis`). [type] is
-  /// the static type of the callback. [boxExternRef] determines if the
-  /// trampoline should box the arguments and return value or convert every
-  /// value. [needsCastClosure] determines if a cast closure is needed in order
-  /// to validate the types of some arguments. [captureThis] determines if
-  /// `this` needs to be passed into the trampoline from the JS wrapper.
+  /// `Function.toJS` or `Function.toJSCaptureThis`). [type] is the static type
+  /// of the callback. [boxExternRef] determines if the trampoline should box
+  /// the arguments and return value or convert every value. [needsCastClosure]
+  /// determines if a cast closure is needed in order to validate the types of
+  /// some arguments. [captureThis] determines if `this` needs to be passed into
+  /// the trampoline from the JS wrapper.
   ///
   /// The procedure will call a JS method that will create a wrapper, cache the
   /// callback, and call the trampoline function with the callback, the JS

pkg/front_end/testcases/dart2js/js_interop_transforms/isa.dart

@@ -45,11 +45,13 @@ void test(JSAny any, JSAny? nullableAny, Object obj, Object? nullableObj) {
 
   any.isA<JSArray>();
   obj.isA<JSArray?>();
-  // JSTypedArray and JSBoxedDartObject handled differently.
+  // Check that there's a specific lowering for some JS types.
   any.isA<JSTypedArray>();
   any.isA<JSBoxedDartObject>();
+  any.isA<JSExportedDartFunction>();
   obj.isA<JSTypedArray>();
   obj.isA<JSBoxedDartObject>();
+  obj.isA<JSExportedDartFunction>();
 
   // User-defined types.
   any.isA<CustomJSAny>();

pkg/front_end/testcases/dart2js/js_interop_transforms/isa.dart.strong.expect

@@ -76,8 +76,10 @@ static method test(js_::JSAny /* erasure=core::Object */ any, js_::JSAny? /* era
   js_::NullableObjectUtilExtension|isA<js_::JSArray<js_::JSAny? /* erasure=core::Object? */>? /* erasure=_interceptors::JSArray<core::Object?>? */>(obj);
   js_::NullableObjectUtilExtension|isA<js_::JSTypedArray /* erasure=dart.typed_data.implementation::NativeTypedData */>(any);
   js_::NullableObjectUtilExtension|isA<js_::JSBoxedDartObject /* erasure=_interceptors::JSObject */>(any);
+  js_::NullableObjectUtilExtension|isA<js_::JSExportedDartFunction /* erasure=_interceptors::JavaScriptFunction */>(any);
   js_::NullableObjectUtilExtension|isA<js_::JSTypedArray /* erasure=dart.typed_data.implementation::NativeTypedData */>(obj);
   js_::NullableObjectUtilExtension|isA<js_::JSBoxedDartObject /* erasure=_interceptors::JSObject */>(obj);
+  js_::NullableObjectUtilExtension|isA<js_::JSExportedDartFunction /* erasure=_interceptors::JavaScriptFunction */>(obj);
   js_::NullableObjectUtilExtension|isA<self::CustomJSAny /* erasure=core::Object */>(any);
   js_::NullableObjectUtilExtension|isA<self::CustomJSObject /* erasure=_interceptors::JSObject */>(any);
   js_::NullableObjectUtilExtension|isA<self::CustomTypedArray /* erasure=dart.typed_data.implementation::NativeTypedData */>(any);

pkg/front_end/testcases/dart2js/js_interop_transforms/isa.dart.strong.modular.expect

@@ -76,8 +76,10 @@ static method test(js_::JSAny /* erasure=core::Object */ any, js_::JSAny? /* era
   js_::NullableObjectUtilExtension|isA<js_::JSArray<js_::JSAny? /* erasure=core::Object? */>? /* erasure=_interceptors::JSArray<core::Object?>? */>(obj);
   js_::NullableObjectUtilExtension|isA<js_::JSTypedArray /* erasure=dart.typed_data.implementation::NativeTypedData */>(any);
   js_::NullableObjectUtilExtension|isA<js_::JSBoxedDartObject /* erasure=_interceptors::JSObject */>(any);
+  js_::NullableObjectUtilExtension|isA<js_::JSExportedDartFunction /* erasure=_interceptors::JavaScriptFunction */>(any);
   js_::NullableObjectUtilExtension|isA<js_::JSTypedArray /* erasure=dart.typed_data.implementation::NativeTypedData */>(obj);
   js_::NullableObjectUtilExtension|isA<js_::JSBoxedDartObject /* erasure=_interceptors::JSObject */>(obj);
+  js_::NullableObjectUtilExtension|isA<js_::JSExportedDartFunction /* erasure=_interceptors::JavaScriptFunction */>(obj);
   js_::NullableObjectUtilExtension|isA<self::CustomJSAny /* erasure=core::Object */>(any);
   js_::NullableObjectUtilExtension|isA<self::CustomJSObject /* erasure=_interceptors::JSObject */>(any);
   js_::NullableObjectUtilExtension|isA<self::CustomTypedArray /* erasure=dart.typed_data.implementation::NativeTypedData */>(any);

pkg/front_end/testcases/dart2js/js_interop_transforms/isa.dart.strong.transformed.expect

@@ -77,8 +77,10 @@ static method test(js_::JSAny /* erasure=core::Object */ any, js_::JSAny? /* era
   obj == null || js_::_isJSAny(obj) && js_::JSAnyUtilityExtension|instanceOfString(obj as js_::JSAny? /* erasure=core::Object? */, "Array");
   !(any == null) && js_::JSAnyUtilityExtension|instanceof(any, js_2::JSObjectUnsafeUtilExtension|callMethodVarArgs<js_::JSFunction /* erasure=_interceptors::JavaScriptFunction */>(js_2::JSObjectUnsafeUtilExtension|[](js_::globalContext, "Object") as js_::JSObject /* erasure=_interceptors::JSObject */, js_::StringToJSString|get#toJS("getPrototypeOf"), <js_::JSAny? /* erasure=core::Object? */>[js_2::JSObjectUnsafeUtilExtension|[](js_::globalContext, "Int8Array") as js_::JSObject /* erasure=_interceptors::JSObject */]));
   js_::_isJSBoxedDartObject(any);
+  js_::_isJSExportedDartFunction(any);
   !(obj == null) && (js_::_isJSAny(obj) && js_::JSAnyUtilityExtension|instanceof(obj as js_::JSAny? /* erasure=core::Object? */, js_2::JSObjectUnsafeUtilExtension|callMethodVarArgs<js_::JSFunction /* erasure=_interceptors::JavaScriptFunction */>(js_2::JSObjectUnsafeUtilExtension|[](js_::globalContext, "Object") as js_::JSObject /* erasure=_interceptors::JSObject */, js_::StringToJSString|get#toJS("getPrototypeOf"), <js_::JSAny? /* erasure=core::Object? */>[js_2::JSObjectUnsafeUtilExtension|[](js_::globalContext, "Int8Array") as js_::JSObject /* erasure=_interceptors::JSObject */])));
   js_::_isJSBoxedDartObject(obj);
+  js_::_isJSExportedDartFunction(obj);
   !(any == null) && js_::JSAnyUtilityExtension|instanceOfString(any, "library1.CustomJSAny");
   !(any == null) && js_::JSAnyUtilityExtension|instanceOfString(any, "library1.CustomJSObject");
   !(any == null) && js_::JSAnyUtilityExtension|instanceOfString(any, "library1.CustomTypedArray");

sdk/lib/_internal/js_dev_runtime/patch/js_allow_interop_patch.dart

@@ -4,7 +4,7 @@
 
 // Patch file for dart:js_util library.
 import 'dart:_foreign_helper' show JS;
-import 'dart:_interceptors' show JavaScriptFunction;
+import 'dart:_interceptors' show functionToJSProperty, JavaScriptFunction;
 import 'dart:_internal' show patch;
 import 'dart:_runtime' as dart;
 
@@ -50,12 +50,6 @@ Function allowInteropCaptureThis(Function f) {
   return ret;
 }
 
-// TODO(srujzs): In dart2js, this is guaranteed to be unique per isolate. DDC
-// doesn't have a mechanism to guarantee that, so use a Symbol instead to match
-// the unique-per-runtime semantics of [allowInterop].
-final _functionToJSPropertyName = r'_$dart_dartClosure';
-final _functionToJSProperty = JS('!', "Symbol($_functionToJSPropertyName)");
-
 JavaScriptFunction _functionToJS0(Function f) {
   // This can only happen if a user casted a JavaScriptFunction to Function.
   // Such a cast is an error in dart2wasm, so we should make this behavior an
@@ -73,7 +67,7 @@ JavaScriptFunction _functionToJS0(Function f) {
     _callDartFunctionFast0,
     f,
   );
-  JS('', '#[#] = #', ret, _functionToJSProperty, f);
+  JS('', '#[#] = #', ret, functionToJSProperty, f);
   return ret;
 }
 
@@ -91,7 +85,7 @@ JavaScriptFunction _functionToJS1(Function f) {
     _callDartFunctionFast1,
     f,
   );
-  JS('', '#[#] = #', ret, _functionToJSProperty, f);
+  JS('', '#[#] = #', ret, functionToJSProperty, f);
   return ret;
 }
 
@@ -109,7 +103,7 @@ JavaScriptFunction _functionToJS2(Function f) {
     _callDartFunctionFast2,
     f,
   );
-  JS('', '#[#] = #', ret, _functionToJSProperty, f);
+  JS('', '#[#] = #', ret, functionToJSProperty, f);
   return ret;
 }
 
@@ -127,7 +121,7 @@ JavaScriptFunction _functionToJS3(Function f) {
     _callDartFunctionFast3,
     f,
   );
-  JS('', '#[#] = #', ret, _functionToJSProperty, f);
+  JS('', '#[#] = #', ret, functionToJSProperty, f);
   return ret;
 }
 
@@ -145,7 +139,7 @@ JavaScriptFunction _functionToJS4(Function f) {
     _callDartFunctionFast4,
     f,
   );
-  JS('', '#[#] = #', ret, _functionToJSProperty, f);
+  JS('', '#[#] = #', ret, functionToJSProperty, f);
   return ret;
 }
 
@@ -163,7 +157,7 @@ JavaScriptFunction _functionToJS5(Function f) {
     _callDartFunctionFast5,
     f,
   );
-  JS('', '#[#] = #', ret, _functionToJSProperty, f);
+  JS('', '#[#] = #', ret, functionToJSProperty, f);
   return ret;
 }
 
@@ -183,7 +177,7 @@ JavaScriptFunction _functionToJSN(Function f, int maxLength) {
     f,
     maxLength,
   );
-  JS('', '#[#] = #', ret, _functionToJSProperty, f);
+  JS('', '#[#] = #', ret, functionToJSProperty, f);
   return ret;
 }
 
@@ -208,7 +202,7 @@ JavaScriptFunction _functionToJSCaptureThisN(Function f, int maxLength) {
     f,
     maxLength,
   );
-  JS('', '#[#] = #', ret, _functionToJSProperty, f);
+  JS('', '#[#] = #', ret, functionToJSProperty, f);
   return ret;
 }
 
@@ -360,5 +354,5 @@ _callDartFunctionFast5(callback, arg1, arg2, arg3, arg4, arg5, int length) {
 }
 
 Function _jsFunctionToDart(JavaScriptFunction f) {
-  return JS('Function', '#[#]', f, _functionToJSProperty);
+  return JS('Function', '#[#]', f, functionToJSProperty);
 }

sdk/lib/_internal/js_dev_runtime/private/interceptors.dart

@@ -305,6 +305,17 @@ findInterceptorForType(Type? type) {}
 /// the dart:rti library because stores information used for type checks.
 class JavaScriptFunction extends LegacyJavaScriptObject implements Function {}
 
+// TODO(srujzs): In dart2js, this is guaranteed to be unique per isolate. DDC
+// doesn't have a mechanism to guarantee that, so use a Symbol instead to match
+// the unique-per-runtime semantics of [allowInterop].
+final _functionToJSPropertyName = r'_$dart_dartClosure';
+final functionToJSProperty = JS('!', "Symbol($_functionToJSPropertyName)");
+
+/// Returns whether [f] is a wrapped Dart function through `dart:js_interop`'s
+/// conversion methods.
+bool isJSExportedDartFunction(JavaScriptFunction f) =>
+    JS('', '#.#', f, functionToJSProperty) != null;
+
 /// Interceptor for JavaScript BigInt primitive values, i.e. values `x` for
 /// which `typeof x == "bigint"`.
 @JsPeerInterface(name: 'BigInt')

sdk/lib/_internal/js_runtime/lib/interceptors.dart

@@ -79,6 +79,17 @@ final String DART_CLOSURE_PROPERTY_NAME = getIsolateAffinityTag(
   r'_$dart_dartClosure',
 );
 
+/// Present in JS functions that were converted specifically using
+/// `dart:js_interop`.
+final String DART_CLOSURE_DART_JSINTEROP_PROPERTY_NAME = getIsolateAffinityTag(
+  r'_$dart_dartClosure_dartJSInterop',
+);
+
+/// Returns whether [f] is a wrapped Dart function through `dart:js_interop`'s
+/// conversion methods.
+bool isJSExportedDartFunction(JavaScriptFunction f) =>
+    JS('', '#.#', f, DART_CLOSURE_DART_JSINTEROP_PROPERTY_NAME) != null;
+
 getDispatchProperty(object) {
   return JS(
     '',
@@ -484,7 +495,9 @@ final class JavaScriptFunction extends LegacyJavaScriptObject
   const JavaScriptFunction();
 
   String toString() {
-    var dartClosure = JS('', '#.#', this, DART_CLOSURE_PROPERTY_NAME);
+    var dartClosure =
+        JS('', '#.#', this, DART_CLOSURE_PROPERTY_NAME) ??
+        JS('', '#.#', this, DART_CLOSURE_DART_JSINTEROP_PROPERTY_NAME);
     if (dartClosure == null) return super.toString();
     return 'JavaScript function for ${dartClosure.toString()}';
   }

sdk/lib/_internal/js_runtime/lib/js_allow_interop_patch.dart

@@ -5,7 +5,11 @@
 // Patch file for dart:js_util library.
 
 import 'dart:_foreign_helper' show JS, DART_CLOSURE_TO_JS;
-import 'dart:_interceptors' show DART_CLOSURE_PROPERTY_NAME, JavaScriptFunction;
+import 'dart:_interceptors'
+    show
+        DART_CLOSURE_PROPERTY_NAME,
+        DART_CLOSURE_DART_JSINTEROP_PROPERTY_NAME,
+        JavaScriptFunction;
 import 'dart:_internal' show patch;
 import 'dart:_js_helper'
     show
@@ -103,7 +107,7 @@ JavaScriptFunction _functionToJS0(Function f) {
     DART_CLOSURE_TO_JS(_callDartFunctionFast0),
     f,
   );
-  JS('', '#.# = #', result, DART_CLOSURE_PROPERTY_NAME, f);
+  JS('', '#.# = #', result, DART_CLOSURE_DART_JSINTEROP_PROPERTY_NAME, f);
   return result;
 }
 
@@ -123,7 +127,7 @@ JavaScriptFunction _functionToJSCaptureThis0(Function f) {
     DART_CLOSURE_TO_JS(_callDartFunctionFast1),
     f,
   );
-  JS('', '#.# = #', result, DART_CLOSURE_PROPERTY_NAME, f);
+  JS('', '#.# = #', result, DART_CLOSURE_DART_JSINTEROP_PROPERTY_NAME, f);
   return result;
 }
 
@@ -143,7 +147,7 @@ JavaScriptFunction _functionToJS1(Function f) {
     DART_CLOSURE_TO_JS(_callDartFunctionFast1),
     f,
   );
-  JS('', '#.# = #', result, DART_CLOSURE_PROPERTY_NAME, f);
+  JS('', '#.# = #', result, DART_CLOSURE_DART_JSINTEROP_PROPERTY_NAME, f);
   return result;
 }
 
@@ -163,7 +167,7 @@ JavaScriptFunction _functionToJSCaptureThis1(Function f) {
     DART_CLOSURE_TO_JS(_callDartFunctionFast2),
     f,
   );
-  JS('', '#.# = #', result, DART_CLOSURE_PROPERTY_NAME, f);
+  JS('', '#.# = #', result, DART_CLOSURE_DART_JSINTEROP_PROPERTY_NAME, f);
   return result;
 }
 
@@ -183,7 +187,7 @@ JavaScriptFunction _functionToJS2(Function f) {
     DART_CLOSURE_TO_JS(_callDartFunctionFast2),
     f,
   );
-  JS('', '#.# = #', result, DART_CLOSURE_PROPERTY_NAME, f);
+  JS('', '#.# = #', result, DART_CLOSURE_DART_JSINTEROP_PROPERTY_NAME, f);
   return result;
 }
 
@@ -203,7 +207,7 @@ JavaScriptFunction _functionToJSCaptureThis2(Function f) {
     DART_CLOSURE_TO_JS(_callDartFunctionFast3),
     f,
   );
-  JS('', '#.# = #', result, DART_CLOSURE_PROPERTY_NAME, f);
+  JS('', '#.# = #', result, DART_CLOSURE_DART_JSINTEROP_PROPERTY_NAME, f);
   return result;
 }
 
@@ -223,7 +227,7 @@ JavaScriptFunction _functionToJS3(Function f) {
     DART_CLOSURE_TO_JS(_callDartFunctionFast3),
     f,
   );
-  JS('', '#.# = #', result, DART_CLOSURE_PROPERTY_NAME, f);
+  JS('', '#.# = #', result, DART_CLOSURE_DART_JSINTEROP_PROPERTY_NAME, f);
   return result;
 }
 
@@ -243,7 +247,7 @@ JavaScriptFunction _functionToJSCaptureThis3(Function f) {
     DART_CLOSURE_TO_JS(_callDartFunctionFast4),
     f,
   );
-  JS('', '#.# = #', result, DART_CLOSURE_PROPERTY_NAME, f);
+  JS('', '#.# = #', result, DART_CLOSURE_DART_JSINTEROP_PROPERTY_NAME, f);
   return result;
 }
 
@@ -263,7 +267,7 @@ JavaScriptFunction _functionToJS4(Function f) {
     DART_CLOSURE_TO_JS(_callDartFunctionFast4),
     f,
   );
-  JS('', '#.# = #', result, DART_CLOSURE_PROPERTY_NAME, f);
+  JS('', '#.# = #', result, DART_CLOSURE_DART_JSINTEROP_PROPERTY_NAME, f);
   return result;
 }
 
@@ -283,7 +287,7 @@ JavaScriptFunction _functionToJSCaptureThis4(Function f) {
     DART_CLOSURE_TO_JS(_callDartFunctionFast5),
     f,
   );
-  JS('', '#.# = #', result, DART_CLOSURE_PROPERTY_NAME, f);
+  JS('', '#.# = #', result, DART_CLOSURE_DART_JSINTEROP_PROPERTY_NAME, f);
   return result;
 }
 
@@ -303,7 +307,7 @@ JavaScriptFunction _functionToJS5(Function f) {
     DART_CLOSURE_TO_JS(_callDartFunctionFast5),
     f,
   );
-  JS('', '#.# = #', result, DART_CLOSURE_PROPERTY_NAME, f);
+  JS('', '#.# = #', result, DART_CLOSURE_DART_JSINTEROP_PROPERTY_NAME, f);
   return result;
 }
 
@@ -325,7 +329,7 @@ JavaScriptFunction _functionToJSN(Function f, int maxLength) {
     f,
     maxLength,
   );
-  JS('', '#.# = #', result, DART_CLOSURE_PROPERTY_NAME, f);
+  JS('', '#.# = #', result, DART_CLOSURE_DART_JSINTEROP_PROPERTY_NAME, f);
   return result;
 }
 
@@ -353,7 +357,7 @@ JavaScriptFunction _functionToJSCaptureThisN(Function f, int maxLength) {
     f,
     maxLength,
   );
-  JS('', '#.# = #', result, DART_CLOSURE_PROPERTY_NAME, f);
+  JS('', '#.# = #', result, DART_CLOSURE_DART_JSINTEROP_PROPERTY_NAME, f);
   return result;
 }
 
@@ -407,5 +411,5 @@ _callDartFunctionFastN(Function callback, List arguments) {
 }
 
 Function _jsFunctionToDart(JavaScriptFunction f) {
-  return JS('Function', '#.#', f, DART_CLOSURE_PROPERTY_NAME);
+  return JS('Function', '#.#', f, DART_CLOSURE_DART_JSINTEROP_PROPERTY_NAME);
 }

sdk/lib/_internal/js_shared/lib/js_interop_patch.dart

@@ -3,7 +3,12 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:_foreign_helper' as foreign_helper;
-import 'dart:_interceptors' show Interceptor, JavaScriptObject;
+import 'dart:_interceptors'
+    show
+        Interceptor,
+        JavaScriptFunction,
+        JavaScriptObject,
+        isJSExportedDartFunction;
 import 'dart:_internal' show patch;
 import 'dart:_js_helper' show createObjectLiteral, staticInteropGlobalContext;
 import 'dart:_js_types';
@@ -130,6 +135,14 @@ bool _isJSObject(Object? any) =>
 @pragma('dart2js:prefer-inline')
 bool _isNullableJSObject(Object? any) => any == null || _isJSObject(any);
 
+@pragma('dart2js:prefer-inline')
+bool _isJSExportedDartFunction(Object? any) =>
+    any is JavaScriptFunction && isJSExportedDartFunction(any);
+
+@pragma('dart2js:prefer-inline')
+bool _isNullableJSExportedDartFunction(Object? any) =>
+    any == null || _isJSExportedDartFunction(any);
+
 // -----------------------------------------------------------------------------
 // JSBoxedDartObject <-> Object
 @patch

sdk/lib/_internal/wasm/lib/js_interop_patch.dart

@@ -266,6 +266,13 @@ bool _isJSObject(Object? any) =>
 
 bool _isNullableJSObject(Object? any) => any == null || _isJSObject(any);
 
+bool _isJSExportedDartFunction(Object? any) =>
+    _isJSAny(any) &&
+    js_helper.isJSWrappedDartFunction(unsafeCast<JSAny>(any).toExternRef);
+
+bool _isNullableJSExportedDartFunction(Object? any) =>
+    any == null || _isJSExportedDartFunction(any);
+
 // -----------------------------------------------------------------------------
 // JSBoxedDartObject <-> Object
 @patch

sdk/lib/js_interop/js_interop.dart

@@ -888,6 +888,10 @@ extension NullableObjectUtilExtension on Object? {
   /// - `JSObject`: `isA<JSObject>` will call an intrinsic function to check
   ///   that the value is a JS object (`instanceof Object` is insufficient for
   ///   some objects).
+  /// - `JSExportedDartFunction`: `isA<JSExportedDartFunction>` will check if
+  ///   the value is a result of a previous
+  ///   [FunctionToJSExportedDartFunction.toJS] or
+  ///   [FunctionToJSExportedDartFunction.toJSCaptureThis] call.
   /// - User interop types whose representation types are JS primitive types:
   ///   This will result in an error to avoid confusion on whether the user
   ///   interop type is used in the type-check. Use the primitive JS type as the

tests/lib/js/static_interop_test/isa/isa_test.dart

@@ -43,9 +43,15 @@ extension type ArraySubtype._(JSArray _) implements JSObject {
 extension type WrapJSBoxedDartObject(JSBoxedDartObject _)
     implements JSBoxedDartObject {}
 
+extension type WrapJSExportedDartFunction(JSExportedDartFunction _)
+    implements JSExportedDartFunction {}
+
 @JS('WrapJSBoxedDartObject.prototype')
 external JSObject get wrapJSBoxedDartObjectPrototype;
 
+@JS('WrapJSExportedDartFunction.prototype')
+external JSObject get wrapJSExportedDartFunctionPrototype;
+
 @JS('Object.setPrototypeOf')
 external void setPrototypeOf(JSObject obj, JSObject prototype);
 
@@ -100,19 +106,23 @@ void testNull() {
   Expect.isTrue(nil.isA<JSObject?>());
   Expect.isTrue(nil.isA<JSAny?>());
   Expect.isTrue(nil.isA<JSBoxedDartObject?>());
+  Expect.isTrue(nil.isA<JSExportedDartFunction?>());
   Expect.isFalse(nil.isA<JSString>());
   Expect.isFalse(nil.isA<JSObject>());
   Expect.isFalse(nil.isA<JSAny>());
   Expect.isFalse(nil.isA<JSBoxedDartObject>());
+  Expect.isFalse(nil.isA<JSExportedDartFunction>());
   Object? nilObj = null;
   Expect.isTrue(nilObj.isA<JSString?>());
   Expect.isTrue(nilObj.isA<JSObject?>());
   Expect.isTrue(nilObj.isA<JSAny?>());
   Expect.isTrue(nilObj.isA<JSBoxedDartObject?>());
+  Expect.isTrue(nilObj.isA<JSExportedDartFunction?>());
   Expect.isFalse(nilObj.isA<JSString>());
   Expect.isFalse(nilObj.isA<JSObject>());
   Expect.isFalse(nilObj.isA<JSAny>());
   Expect.isFalse(nilObj.isA<JSBoxedDartObject>());
+  Expect.isFalse(nilObj.isA<JSExportedDartFunction>());
   // JS nullish values should behave no differently.
   eval('''
     globalThis.nullable = null;
@@ -121,10 +131,12 @@ void testNull() {
   Expect.isTrue(nullable.isA<JSObject?>());
   Expect.isTrue(nullable.isA<JSAny?>());
   Expect.isTrue(nullable.isA<JSBoxedDartObject?>());
+  Expect.isTrue(nullable.isA<JSExportedDartFunction?>());
   Expect.isFalse(nullable.isA<JSString>());
   Expect.isFalse(nullable.isA<JSObject>());
   Expect.isFalse(nullable.isA<JSAny>());
   Expect.isFalse(nullable.isA<JSBoxedDartObject>());
+  Expect.isFalse(nullable.isA<JSExportedDartFunction>());
   eval('''
     globalThis.nullable = undefined;
   ''');
@@ -132,10 +144,12 @@ void testNull() {
   Expect.isTrue(nullable.isA<JSObject?>());
   Expect.isTrue(nullable.isA<JSAny?>());
   Expect.isTrue(nullable.isA<JSBoxedDartObject?>());
+  Expect.isTrue(nullable.isA<JSExportedDartFunction?>());
   Expect.isFalse(nullable.isA<JSString>());
   Expect.isFalse(nullable.isA<JSObject>());
   Expect.isFalse(nullable.isA<JSAny>());
   Expect.isFalse(nullable.isA<JSBoxedDartObject>());
+  Expect.isFalse(nullable.isA<JSExportedDartFunction>());
 }
 
 void testPrimitives() {
@@ -292,14 +306,12 @@ void testJSObjects() {
   Expect.isTrue(jsFunction.isA<JSFunction?>());
   testIsJSObject(jsFunction);
   Expect.isFalse(jsFunction.isA<JSNumber>());
-  // TODO(srujzs): Currently, we can't distinguish between a JS function and an
-  // exported function. https://github.com/dart-lang/sdk/issues/62573
-  Expect.isTrue(jsFunction.isA<JSExportedDartFunction>());
+  Expect.isFalse(jsFunction.isA<JSExportedDartFunction>());
 
   Object jsFunctionObj = jsFunction;
   Expect.isTrue(jsFunctionObj.isA<JSFunction>());
   Expect.isFalse(jsFunctionObj.isA<JSBoxedDartObject>());
-  Expect.isTrue(jsFunctionObj.isA<JSExportedDartFunction>());
+  Expect.isFalse(jsFunctionObj.isA<JSExportedDartFunction>());
 
   // JSExportedDartFunction.
   final jsExportedDartFunction = () {}.toJS;
@@ -526,6 +538,22 @@ void testUserTypes() {
   Expect.isTrue(wrapJsBox.isA<WrapJSBoxedDartObject?>());
   Expect.isTrue(wrapJsBoxObj.isA<WrapJSBoxedDartObject>());
 
+  // Test that a type wrapping `JSExportedDartFunction` should have a different
+  // type-check.
+  eval('''
+    class WrapJSExportedDartFunction {}
+    globalThis.WrapJSExportedDartFunction = WrapJSExportedDartFunction;
+  ''');
+  final wrapJsEdf = WrapJSExportedDartFunction(() {}.toJS);
+  Expect.isFalse(wrapJsEdf.isA<WrapJSExportedDartFunction>());
+  setPrototypeOf(wrapJsEdf, wrapJSExportedDartFunctionPrototype);
+  Expect.isTrue(wrapJsEdf.isA<WrapJSExportedDartFunction>());
+  Expect.isTrue(nil.isA<WrapJSExportedDartFunction?>());
+  Expect.isFalse(nil.isA<WrapJSExportedDartFunction>());
+
+  Object? wrapJsEdfObj = wrapJsEdf;
+  Expect.isTrue(wrapJsEdfObj.isA<WrapJSExportedDartFunction>());
+
   // Test subtyping a type in the browser.
   eval('''
     class SubtypeArray extends Array {}