Add react lazy

example/suspense/suspense.dart

@@ -1,55 +1,40 @@
 @JS()
-library js_components;
+library example.suspense.suspense;
 
 import 'dart:html';
-import 'dart:js_util';
 
 import 'package:js/js.dart';
+import 'package:react/hooks.dart';
 import 'package:react/react.dart' as react;
-import 'package:react/react_client.dart';
 import 'package:react/react_client/react_interop.dart';
 import 'package:react/react_dom.dart' as react_dom;
-import 'package:react/src/js_interop_util.dart';
 import './simple_component.dart' deferred as simple;
 
-@JS('React.lazy')
-external ReactClass jsLazy(Promise Function() factory);
-
-// Only intended for testing purposes, Please do not copy/paste this into repo.
-// This will most likely be added to the PUBLIC api in the future,
-// but needs more testing and Typing decisions to be made first.
-ReactJsComponentFactoryProxy lazy(Future<ReactComponentFactoryProxy> Function() factory) =>
-    ReactJsComponentFactoryProxy(
-      jsLazy(
-        allowInterop(
-          () => futureToPromise(
-            // React.lazy only supports "default exports" from a module.
-            // This `{default: yourExport}` workaround can be found in the React.lazy RFC comments.
-            // See: https://github.com/reactjs/rfcs/pull/64#issuecomment-431507924
-            (() async => jsify({'default': (await factory()).type}))(),
-          ),
-        ),
-      ),
-    );
-
 main() {
   final content = wrapper({});
 
   react_dom.render(content, querySelector('#content'));
 }
 
 final lazyComponent = lazy(() async {
-  await simple.loadLibrary();
   await Future.delayed(Duration(seconds: 5));
+  await simple.loadLibrary();
+
   return simple.SimpleComponent;
 });
 
 var wrapper = react.registerFunctionComponent(WrapperComponent, displayName: 'wrapper');
 
 WrapperComponent(Map props) {
+  final showComponent = useState(false);
   return react.div({
     'id': 'lazy-wrapper'
   }, [
-    react.Suspense({'fallback': 'Loading...'}, [lazyComponent({})])
+    react.button({
+      'onClick': (_) {
+        showComponent.set(!showComponent.value);
+      }
+    }, 'Toggle component'),
+    react.Suspense({'fallback': 'Loading...'}, showComponent.value ? lazyComponent({}) : null)
   ]);
 }

lib/react.dart

@@ -21,7 +21,7 @@ import 'package:react/src/react_client/private_utils.dart' show validateJsApi, v
 export 'package:react/src/context.dart';
 export 'package:react/src/prop_validator.dart';
 export 'package:react/src/react_client/event_helpers.dart';
-export 'package:react/react_client/react_interop.dart' show forwardRef2, createRef, memo2;
+export 'package:react/react_client/react_interop.dart' show forwardRef2, createRef, memo2, lazy;
 export 'package:react/src/react_client/synthetic_event_wrappers.dart' hide NonNativeDataTransfer;
 export 'package:react/src/react_client/synthetic_data_transfer.dart' show SyntheticDataTransfer;
 

lib/react_client/react_interop.dart

@@ -19,6 +19,8 @@ import 'package:react/react_client/component_factory.dart' show ReactDartWrapped
 import 'package:react/src/react_client/dart2_interop_workaround_bindings.dart';
 import 'package:react/src/typedefs.dart';
 
+import '../src/js_interop_util.dart';
+
 typedef ReactJsComponentFactory = ReactElement Function(dynamic props, dynamic children);
 
 // ----------------------------------------------------------------------------
@@ -42,6 +44,7 @@ abstract class React {
     dynamic wrapperFunction, [
     bool Function(JsMap prevProps, JsMap nextProps)? areEqual,
   ]);
+  external static ReactClass lazy(Promise Function() load);
 
   external static bool isValidElement(dynamic object);
 
@@ -274,6 +277,52 @@ ReactComponentFactoryProxy memo2(ReactComponentFactoryProxy factory,
   return ReactDartWrappedComponentFactoryProxy(hoc);
 }
 
+/// Defer loading a component's code until it is rendered for the first time.
+///
+/// The `lazy` function is used to create lazy components in react-dart. Lazy components are able to run asynchronous code only when they are trying to be rendered for the first time, allowing for deferred loading of the component's code.
+///
+/// To use the `lazy` function, you need to wrap the lazy component with a `Suspense` component. The `Suspense` component allows you to specify what should be displayed while the lazy component is loading, such as a loading spinner or a placeholder.
+///
+/// Example usage:
+/// ```dart
+/// import 'package:react/react.dart' show lazy, Suspense;
+/// import './simple_component.dart' deferred as simple;
+///
+/// final lazyComponent = lazy(() async {
+///   await simple.loadLibrary();
+///   return simple.SimpleComponent;
+/// });
+///
+/// // Wrap the lazy component with Suspense
+/// final app = Suspense(
+///   {
+///     fallback: 'Loading...',
+///   },
+///   lazyComponent({}),
+/// );
+/// ```
+///
+/// Defer loading a component’s code until it is rendered for the first time.
+///
+/// Lazy components need to be wrapped with `Suspense` to render.
+/// `Suspense` also allows you to specify what should be displayed while the lazy component is loading.
+ReactComponentFactoryProxy lazy(Future<ReactComponentFactoryProxy> Function() load) {
+  final hoc = React.lazy(
+    allowInterop(
+      () => futureToPromise(
+        (() async {
+          final factory = await load();
+          return jsify({'default': factory.type});
+        })(),
+      ),
+    ),
+  );
+
+  setProperty(hoc, 'dartComponentVersion', ReactDartComponentVersion.component2);
+
+  return ReactDartWrappedComponentFactoryProxy(hoc);
+}
+
 abstract class ReactDom {
   static Element? findDOMNode(ReactNode object) => ReactDOM.findDOMNode(object);
   static dynamic render(ReactNode component, Element element) => ReactDOM.render(component, element);

test/factory/common_factory_tests.dart

@@ -26,10 +26,12 @@ import '../util.dart';
 /// [dartComponentVersion] should be specified for all components with Dart render code in order to
 /// properly test `props.children`, forwardRef compatibility, etc.
 void commonFactoryTests(ReactComponentFactoryProxy factory,
-    {String? dartComponentVersion, bool skipPropValuesTest = false}) {
+    {String? dartComponentVersion,
+    bool skipPropValuesTest = false,
+    ReactElement Function(dynamic children)? renderWrapper}) {
   _childKeyWarningTests(
     factory,
-    renderWithUniqueOwnerName: _renderWithUniqueOwnerName,
+    renderWithUniqueOwnerName: (ReactElement Function() render) => _renderWithUniqueOwnerName(render, renderWrapper),
   );
 
   test('renders an instance with the corresponding `type`', () {
@@ -532,7 +534,7 @@ void _childKeyWarningTests(ReactComponentFactoryProxy factory,
     });
 
     test('warns when a single child is passed as a list', () {
-      _renderWithUniqueOwnerName(() => factory({}, [react.span({})]));
+      renderWithUniqueOwnerName(() => factory({}, [react.span({})]));
 
       expect(consoleErrorCalled, isTrue, reason: 'should have outputted a warning');
       expect(consoleErrorMessage, contains('Each child in a list should have a unique "key" prop.'));
@@ -577,12 +579,12 @@ int _nextFactoryId = 0;
 /// Renders the provided [render] function with a Component2 owner that will have a unique name.
 ///
 /// This prevents React JS from not printing key warnings it deems as "duplicates".
-void _renderWithUniqueOwnerName(ReactElement Function() render) {
+void _renderWithUniqueOwnerName(ReactElement Function() render, [ReactElement Function(dynamic)? wrapper]) {
   final factory = react.registerComponent2(() => _UniqueOwnerHelperComponent());
   factory.reactClass.displayName = 'OwnerHelperComponent_$_nextFactoryId';
   _nextFactoryId++;
 
-  rtu.renderIntoDocument(factory({'render': render}));
+  rtu.renderIntoDocument(factory({'render': wrapper != null ? () => wrapper(render()) : render}));
 }
 
 class _UniqueOwnerHelperComponent extends react.Component2 {

test/react_lazy_test.dart

@@ -0,0 +1,26 @@
+@TestOn('browser')
+library react.react_lazy_test;
+
+import 'package:react/react.dart' as react;
+import 'package:react/react_client/react_interop.dart';
+import 'package:test/test.dart';
+
+import 'factory/common_factory_tests.dart';
+
+main() {
+  group('lazy', () {
+    group('- common factory behavior -', () {
+      final LazyTest = react.lazy(() async => react.registerFunctionComponent((props) {
+            props['onDartRender']?.call(props);
+            return react.div({...props});
+          }));
+
+      commonFactoryTests(
+        LazyTest,
+        // ignore: invalid_use_of_protected_member
+        dartComponentVersion: ReactDartComponentVersion.component2,
+        renderWrapper: (child) => react.Suspense({'fallback': 'Loading...'}, child),
+      );
+    });
+  });
+}

test/react_lazy_test.html

@@ -0,0 +1,12 @@
+<!DOCTYPE html>
+<html>
+  <head lang="en">
+    <meta charset="UTF-8" />
+    <title></title>
+    <script src="packages/react/react_with_addons.js"></script>
+    <script src="packages/react/react_dom.js"></script>
+    <link rel="x-dart-test" href="react_lazy_test.dart" />
+    <script src="packages/test/dart.js"></script>
+  </head>
+  <body></body>
+</html>

test/react_suspense_test.dart

@@ -3,39 +3,15 @@
 library react_test_utils_test;
 
 import 'dart:html';
-import 'dart:js_util';
 
 import 'package:js/js.dart';
 import 'package:react/react.dart' as react;
-import 'package:react/react.dart';
-import 'package:react/react_client/component_factory.dart';
 import 'package:react/react_client/react_interop.dart';
 import 'package:react/react_dom.dart' as react_dom;
-import 'package:react/src/js_interop_util.dart';
 import 'package:test/test.dart';
 
 import './react_suspense_lazy_component.dart' deferred as simple;
 
-@JS('React.lazy')
-external ReactClass jsLazy(Promise Function() factory);
-
-// Only intended for testing purposes, Please do not copy/paste this into repo.
-// This will most likely be added to the PUBLIC api in the future,
-// but needs more testing and Typing decisions to be made first.
-ReactJsComponentFactoryProxy lazy(Future<ReactComponentFactoryProxy> Function() factory) =>
-    ReactJsComponentFactoryProxy(
-      jsLazy(
-        allowInterop(
-          () => futureToPromise(
-            // React.lazy only supports "default exports" from a module.
-            // This `{default: yourExport}` workaround can be found in the React.lazy RFC comments.
-            // See: https://github.com/reactjs/rfcs/pull/64#issuecomment-431507924
-            (() async => jsify({'default': (await factory()).type}))(),
-          ),
-        ),
-      ),
-    );
-
 main() {
   group('Suspense', () {
     test('renders fallback UI first followed by the real component', () async {