[web] Hide JS types from dart:ui_web (#42252)

In order to use the exported `PlatformLocation` cross-platform, we need to remove any JS types from the interface. Namely, `DomEventListener`.

Required by flutter/flutter#126851

Author: mdebbar

lib/web_ui/lib/src/engine/dom.dart

@@ -2119,7 +2119,7 @@ extension DomHistoryExtension on DomHistory {
   external JSVoid _go1();
   @JS('go')
   external JSVoid _go2(JSNumber delta);
-  void go([double? delta]) {
+  void go([int? delta]) {
     if (delta == null) {
       _go1();
     } else {

lib/web_ui/lib/ui_web/src/ui_web/navigation/platform_location.dart

@@ -2,10 +2,14 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'package:meta/meta.dart';
 import 'package:ui/src/engine.dart';
 
 import 'url_strategy.dart';
 
+/// Function type that handles pop state events.
+typedef EventListener = dynamic Function(Object event);
+
 /// Encapsulates all calls to DOM apis, which allows the [UrlStrategy] classes
 /// to be platform agnostic and testable.
 ///
@@ -15,13 +19,13 @@ abstract interface class PlatformLocation {
   /// Registers an event listener for the `popstate` event.
   ///
   /// See: https://developer.mozilla.org/en-US/docs/Web/API/WindowEventHandlers/onpopstate
-  void addPopStateListener(DomEventListener fn);
+  void addPopStateListener(EventListener fn);
 
   /// Unregisters the given listener (added by [addPopStateListener]) from the
   /// `popstate` event.
   ///
   /// See: https://developer.mozilla.org/en-US/docs/Web/API/WindowEventHandlers/onpopstate
-  void removePopStateListener(DomEventListener fn);
+  void removePopStateListener(EventListener fn);
 
   /// The `pathname` part of the URL in the browser address bar.
   ///
@@ -64,14 +68,17 @@ abstract interface class PlatformLocation {
   /// * `go(3)` moves forward 3 steps in hisotry.
   ///
   /// See: https://developer.mozilla.org/en-US/docs/Web/API/History/go
-  void go(double count);
+  void go(int count);
 
   /// The base href where the Flutter app is being served.
   ///
   /// See: https://developer.mozilla.org/en-US/docs/Web/HTML/Element/base
   String? getBaseHref();
 }
 
+final Map<EventListener, DomEventListener> _popStateListenersCache =
+    <EventListener, DomEventListener>{};
+
 /// Delegates to real browser APIs to provide platform location functionality.
 class BrowserPlatformLocation implements PlatformLocation {
   /// Default constructor for [BrowserPlatformLocation].
@@ -80,14 +87,24 @@ class BrowserPlatformLocation implements PlatformLocation {
   DomLocation get _location => domWindow.location;
   DomHistory get _history => domWindow.history;
 
+  @visibleForTesting
+  DomEventListener getOrCreateDomEventListener(EventListener fn) {
+    return _popStateListenersCache.putIfAbsent(fn, () => createDomEventListener(fn));
+  }
+
   @override
-  void addPopStateListener(DomEventListener fn) {
-    domWindow.addEventListener('popstate', fn);
+  void addPopStateListener(EventListener fn) {
+    domWindow.addEventListener('popstate', getOrCreateDomEventListener(fn));
   }
 
   @override
-  void removePopStateListener(DomEventListener fn) {
-    domWindow.removeEventListener('popstate', fn);
+  void removePopStateListener(EventListener fn) {
+    assert(
+      _popStateListenersCache.containsKey(fn),
+      'Removing a listener that was never added or was removed already.',
+    );
+    domWindow.removeEventListener('popstate', getOrCreateDomEventListener(fn));
+    _popStateListenersCache.remove(fn);
   }
 
   @override
@@ -113,7 +130,7 @@ class BrowserPlatformLocation implements PlatformLocation {
   }
 
   @override
-  void go(double count) {
+  void go(int count) {
     _history.go(count);
   }
 

lib/web_ui/lib/ui_web/src/ui_web/navigation/url_strategy.dart

@@ -151,10 +151,10 @@ class HashUrlStrategy extends UrlStrategy {
 
   @override
   ui.VoidCallback addPopStateListener(PopStateListener fn) {
-    final DomEventListener wrappedFn = createDomEventListener((DomEvent event) {
+    void wrappedFn(Object event) {
       // `fn` expects `event.state`, not a `DomEvent`.
       fn((event as DomPopStateEvent).state);
-    });
+    }
     _platformLocation.addPopStateListener(wrappedFn);
     return () => _platformLocation.removePopStateListener(wrappedFn);
   }
@@ -199,7 +199,7 @@ class HashUrlStrategy extends UrlStrategy {
 
   @override
   Future<void> go(int count) {
-    _platformLocation.go(count.toDouble());
+    _platformLocation.go(count);
     return _waitForPopState();
   }
 

lib/web_ui/test/engine/history_test.dart

@@ -3,20 +3,19 @@
 // found in the LICENSE file.
 
 import 'dart:async';
-import 'dart:js_interop'
-    show JSExportedDartFunction, JSExportedDartFunctionToFunction;
 
 import 'package:quiver/testing/async.dart';
 import 'package:test/bootstrap/browser.dart';
 import 'package:test/test.dart';
 import 'package:ui/src/engine.dart' show window;
 import 'package:ui/src/engine/dom.dart'
-    show DomEvent, DomEventListener, createDomPopStateEvent;
+    show DomEvent, createDomPopStateEvent;
 import 'package:ui/src/engine/navigation.dart';
 import 'package:ui/src/engine/services.dart';
 import 'package:ui/src/engine/test_embedding.dart';
 import 'package:ui/ui_web/src/ui_web.dart';
 
+import '../common/matchers.dart';
 import '../common/spy.dart';
 
 Map<String, dynamic> _wrapOriginState(dynamic state) {
@@ -690,6 +689,35 @@ void testMain() {
       expect(state, expected);
     });
   });
+
+  group('$BrowserPlatformLocation', () {
+    test('getOrCreateDomEventListener caches funcions', () {
+      const BrowserPlatformLocation location = BrowserPlatformLocation();
+      void myListener(Object event) {}
+
+      expect(
+        identical(
+          location.getOrCreateDomEventListener(myListener),
+          location.getOrCreateDomEventListener(myListener),
+        ),
+        isTrue,
+      );
+    });
+
+    test('throws if removing an invalid listener', () {
+      const BrowserPlatformLocation location = BrowserPlatformLocation();
+      void myAddedListener(Object event) {}
+      void myNonAddedListener(Object event) {}
+
+      location.addPopStateListener(myAddedListener);
+      expect(() => location.removePopStateListener(myAddedListener), returnsNormally);
+      // Removing the same listener twice should throw.
+      expect(() => location.removePopStateListener(myAddedListener), throwsAssertionError);
+
+      // A listener that was never added.
+      expect(() => location.removePopStateListener(myNonAddedListener), throwsAssertionError);
+    });
+  });
 }
 
 Future<void> routeUpdated(String routeName) {
@@ -736,7 +764,7 @@ class TestPlatformLocation implements PlatformLocation {
   @override
   dynamic state;
 
-  List<DomEventListener> popStateListeners = <DomEventListener>[];
+  List<EventListener> popStateListeners = <EventListener>[];
 
   @override
   String pathname = '';
@@ -753,19 +781,18 @@ class TestPlatformLocation implements PlatformLocation {
         if (state != null) 'state': state,
       },
     );
-    for (final DomEventListener listener in popStateListeners) {
-      final Function fn = (listener as JSExportedDartFunction).toDart;
-      fn(event);
+    for (final EventListener listener in popStateListeners) {
+      listener(event);
     }
   }
 
   @override
-  void addPopStateListener(DomEventListener fn) {
+  void addPopStateListener(EventListener fn) {
     popStateListeners.add(fn);
   }
 
   @override
-  void removePopStateListener(DomEventListener fn) {
+  void removePopStateListener(EventListener fn) {
     throw UnimplementedError();
   }
 
@@ -780,7 +807,7 @@ class TestPlatformLocation implements PlatformLocation {
   }
 
   @override
-  void go(double count) {
+  void go(int count) {
     throw UnimplementedError();
   }