CPLAT-8034 Implement/Expose useState Hook

example/test/function_component_test.dart

@@ -1,31 +1,37 @@
 import 'dart:html';
 
+import 'package:react/hooks.dart';
 import 'package:react/react.dart' as react;
 import 'package:react/react_dom.dart' as react_dom;
 import 'package:react/react_client.dart';
 
-import 'react_test_components.dart';
+var useStateTestFunctionComponent = react.registerFunctionComponent(UseStateTestComponent, displayName: 'useStateTest');
+
+UseStateTestComponent(Map props) {
+  final count = useState(0);
+
+  return react.div({}, [
+    count.value,
+    react.button({'onClick': (_) => count.set(0)}, ['Reset']),
+    react.button({
+      'onClick': (_) => count.setWithUpdater((prev) => prev + 1),
+    }, [
+      '+'
+    ]),
+  ]);
+}
 
 void main() {
   setClientConfiguration();
-  var inputValue = 'World';
-  // TODO: replace this with hooks/useState when they are added.
+
   render() {
     react_dom.render(
         react.Fragment({}, [
-          react.input(
-            {
-              'defaultValue': inputValue,
-              'onChange': (event) {
-                inputValue = event.currentTarget.value;
-                render();
-              }
-            },
-          ),
-          react.br({}),
-          helloGregFunctionComponent({'key': 'greg'}),
-          react.br({}),
-          helloGregFunctionComponent({'key': 'not greg'}, inputValue)
+          react.h1({'key': 'functionComponentTestLabel'}, ['Function Component Tests']),
+          react.h2({'key': 'useStateTestLabel'}, ['useState Hook Test']),
+          useStateTestFunctionComponent({
+            'key': 'useStateTest',
+          }, []),
         ]),
         querySelector('#content'));
   }

example/test/react_test_components.dart

@@ -393,16 +393,6 @@ class _NewContextTypeConsumerComponent extends react.Component2 {
   }
 }
 
-var helloGregFunctionComponent = react.registerFunctionComponent(HelloGreg);
-
-HelloGreg(Map props) {
-  var content = ['Hello Greg!'];
-  if (props['children'].isNotEmpty) {
-    content = ['Hello ' + props['children'].join(' ') + '!'];
-  }
-  return react.Fragment({}, content);
-}
-
 class _Component2TestComponent extends react.Component2 with react.TypedSnapshot<String> {
   get defaultProps => {'defaultProp': true};
 

lib/hooks.dart

@@ -0,0 +1,103 @@
+@JS()
+library hooks;
+
+import 'package:js/js.dart';
+import 'package:react/react.dart';
+import 'package:react/react_client/react_interop.dart';
+
+/// The return value of [useState].
+///
+/// The current value of the state is available via [value] and
+/// functions to update it are available via [set] and [setWithUpdater].
+///
+/// Note there are two rules for using Hooks (<https://reactjs.org/docs/hooks-rules.html>):
+///
+/// * Only call Hooks at the top level.
+/// * Only call Hooks from inside a [DartFunctionComponent].
+///
+/// Learn more: <https://reactjs.org/docs/hooks-state.html>.
+class StateHook<T> {
+  /// The first item of the pair returned by [React.useState].
+  T _value;
+
+  /// The second item in the pair returned by [React.useState].
+  void Function(dynamic) _setValue;
+
+  StateHook(T initialValue) {
+    final result = React.useState(initialValue);
+    _value = result[0];
+    _setValue = result[1];
+  }
+
+  /// Constructor for [useStateLazy], calls lazy version of [React.useState] to
+  /// initialize [_value] to the return value of [init].
+  ///
+  /// See: <https://reactjs.org/docs/hooks-reference.html#lazy-initial-state>.
+  StateHook.lazy(T init()) {
+    final result = React.useState(allowInterop(init));
+    _value = result[0];
+    _setValue = result[1];
+  }
+
+  /// The current value of the state.
+  ///
+  /// See: <https://reactjs.org/docs/hooks-reference.html#usestate>.
+  T get value => _value;
+
+  /// Updates [value] to [newValue].
+  ///
+  /// See: <https://reactjs.org/docs/hooks-state.html#updating-state>.
+  void set(T newValue) => _setValue(newValue);
+
+  /// Updates [value] to the return value of [computeNewValue].
+  ///
+  /// See: <https://reactjs.org/docs/hooks-reference.html#functional-updates>.
+  void setWithUpdater(T computeNewValue(T oldValue)) => _setValue(allowInterop(computeNewValue));
+}
+
+/// Adds local state to a [DartFunctionComponent]
+/// by returning a [StateHook] with [StateHook.value] initialized to [initialValue].
+///
+/// > __Note:__ If the [initialValue] is expensive to compute, [useStateLazy] should be used instead.
+///
+/// __Example__:
+///
+/// ```
+/// UseStateTestComponent(Map props) {
+///   final count = useState(0);
+///
+///   return react.div({}, [
+///     count.value,
+///     react.button({'onClick': (_) => count.set(0)}, ['Reset']),
+///     react.button({
+///       'onClick': (_) => count.setWithUpdater((prev) => prev + 1),
+///     }, ['+']),
+///   ]);
+/// }
+/// ```
+///
+/// Learn more: <https://reactjs.org/docs/hooks-state.html>.
+StateHook<T> useState<T>(T initialValue) => StateHook(initialValue);
+
+/// Adds local state to a [DartFunctionComponent]
+/// by returning a [StateHook] with [StateHook.value] initialized to the return value of [init].
+///
+/// __Example__:
+///
+/// ```
+/// UseStateTestComponent(Map props) {
+///   final count = useStateLazy(() {
+///     var initialState = someExpensiveComputation(props);
+///     return initialState;
+///   }));
+///
+///   return react.div({}, [
+///     count.value,
+///     react.button({'onClick': (_) => count.set(0)}, ['Reset']),
+///     react.button({'onClick': (_) => count.set((prev) => prev + 1)}, ['+']),
+///   ]);
+/// }
+/// ```
+///
+/// Learn more: <https://reactjs.org/docs/hooks-reference.html#lazy-initial-state>.
+StateHook<T> useStateLazy<T>(T init()) => StateHook.lazy(init);

lib/react_client/react_interop.dart

@@ -44,6 +44,9 @@ abstract class React {
   external static ReactClass get Fragment;
 
   external static JsRef createRef();
+  external static ReactClass forwardRef(Function(JsMap props, JsRef ref) wrapperFunction);
+
+  external static List<dynamic> useState(dynamic value);
 }
 
 /// Creates a [Ref] object that can be attached to a [ReactElement] via the ref prop.
@@ -108,7 +111,7 @@ class JsRef {
 ///
 /// See: <https://reactjs.org/docs/forwarding-refs.html>.
 ReactJsComponentFactoryProxy forwardRef(Function(Map props, Ref ref) wrapperFunction) {
-  var hoc = _jsForwardRef(allowInterop((JsMap props, JsRef ref) {
+  var hoc = React.forwardRef(allowInterop((JsMap props, JsRef ref) {
     final dartProps = JsBackedMap.backedBy(props);
     final dartRef = Ref.fromJs(ref);
     return wrapperFunction(dartProps, dartRef);
@@ -117,9 +120,6 @@ ReactJsComponentFactoryProxy forwardRef(Function(Map props, Ref ref) wrapperFunc
   return new ReactJsComponentFactoryProxy(hoc, shouldConvertDomProps: false);
 }
 
-@JS('React.forwardRef')
-external ReactClass _jsForwardRef(Function(JsMap props, JsRef ref) wrapperFunction);
-
 abstract class ReactDom {
   static Element findDOMNode(object) => ReactDOM.findDOMNode(object);
   static ReactComponent render(ReactElement component, Element element) => ReactDOM.render(component, element);

test/hooks_test.dart

@@ -0,0 +1,96 @@
+// ignore_for_file: deprecated_member_use_from_same_package
+@TestOn('browser')
+@JS()
+library hooks_test;
+
+import 'dart:html';
+
+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_dom.dart' as react_dom;
+import 'package:react/react_test_utils.dart' as react_test_utils;
+import 'package:test/test.dart';
+
+main() {
+  setClientConfiguration();
+
+  group('React Hooks: ', () {
+    group('useState -', () {
+      ReactDartFunctionComponentFactoryProxy UseStateTest;
+      DivElement textRef;
+      DivElement countRef;
+      ButtonElement setButtonRef;
+      ButtonElement setWithUpdaterButtonRef;
+
+      setUpAll(() {
+        var mountNode = new DivElement();
+
+        UseStateTest = react.registerFunctionComponent((Map props) {
+          final text = useStateLazy(() {
+            return 'initialValue';
+          });
+          final count = useState(0);
+
+          return react.div({}, [
+            react.div({
+              'ref': (ref) {
+                textRef = ref;
+              },
+            }, [
+              text.value
+            ]),
+            react.div({
+              'ref': (ref) {
+                countRef = ref;
+              },
+            }, [
+              count.value
+            ]),
+            react.button({
+              'onClick': (_) => text.set('newValue'),
+              'ref': (ref) {
+                setButtonRef = ref;
+              },
+            }, [
+              'Set'
+            ]),
+            react.button({
+              'onClick': (_) => count.setWithUpdater((prev) => prev + 1),
+              'ref': (ref) {
+                setWithUpdaterButtonRef = ref;
+              },
+            }, [
+              '+'
+            ]),
+          ]);
+        });
+
+        react_dom.render(UseStateTest({}), mountNode);
+      });
+
+      tearDownAll(() {
+        UseStateTest = null;
+      });
+
+      test('initializes state correctly', () {
+        expect(countRef.text, '0');
+      });
+
+      test('Lazy initializes state correctly', () {
+        expect(textRef.text, 'initialValue');
+      });
+
+      test('StateHook.set updates state correctly', () {
+        react_test_utils.Simulate.click(setButtonRef);
+        expect(textRef.text, 'newValue');
+      });
+
+      test('StateHook.setWithUpdater updates state correctly', () {
+        react_test_utils.Simulate.click(setWithUpdaterButtonRef);
+        expect(countRef.text, '1');
+      });
+    });
+  });
+}

test/hooks_test.html

@@ -0,0 +1,13 @@
+<!DOCTYPE html>
+<html>
+<head lang="en">
+    <meta charset="UTF-8">
+    <title></title>
+    <script src="packages/react/react.js"></script>
+    <script src="packages/react/react_dom.js"></script>
+    <link rel="x-dart-test" href="hooks_test.dart">
+    <script src="packages/test/dart.js"></script>
+</head>
+<body>
+</body>
+</html>