feat: add dangerouslyGetState (#63)

packages/core/src/__tests__/index.test.tsx

@@ -4,6 +4,8 @@ import Screen from '../Screen';
 import NavigationContainer from '../NavigationContainer';
 import useNavigationBuilder from '../useNavigationBuilder';
 import MockRouter, { MockRouterKey } from './__fixtures__/MockRouter';
+import useNavigation from '../useNavigation';
+import { NavigationState } from '../types';
 
 beforeEach(() => (MockRouterKey.current = 0));
 
@@ -467,6 +469,7 @@ it('updates route params with setParams applied to parent', () => {
       { key: 'foo', name: 'foo', params: { username: 'alice' } },
       { key: 'bar', name: 'bar' },
     ],
+    stale: false,
   });
 
   act(() => setParams({ age: 25 }));
@@ -480,6 +483,7 @@ it('updates route params with setParams applied to parent', () => {
       { key: 'foo', name: 'foo', params: { username: 'alice', age: 25 } },
       { key: 'bar', name: 'bar' },
     ],
+    stale: false,
   });
 });
 
@@ -519,6 +523,40 @@ it('handles change in route names', () => {
   });
 });
 
+it('gives access to internal state', () => {
+  const TestNavigator = (props: any): any => {
+    const { state, descriptors } = useNavigationBuilder(MockRouter, props);
+
+    return descriptors[state.routes[state.index].key].render();
+  };
+
+  let state: NavigationState | undefined;
+
+  const Test = () => {
+    const navigation = useNavigation();
+    state = navigation.dangerouslyGetState();
+    return null;
+  };
+
+  const root = (
+    <NavigationContainer>
+      <TestNavigator initialRouteName="bar">
+        <Screen name="bar" component={Test} />
+      </TestNavigator>
+    </NavigationContainer>
+  );
+
+  render(root).update(root);
+
+  expect(state).toEqual({
+    index: 0,
+    key: '0',
+    routeNames: ['bar'],
+    routes: [{ key: 'bar', name: 'bar' }],
+    stale: false,
+  });
+});
+
 it("throws if navigator doesn't have any screens", () => {
   const TestNavigator = (props: any) => {
     useNavigationBuilder(MockRouter, props);

packages/core/src/types.tsx

@@ -377,6 +377,13 @@ export type NavigationProp<
   dangerouslyGetParent():
     | NavigationProp<ParamListBase, string, any, any>
     | undefined;
+
+  /**
+   * Returns the navigator's state. Reason why the function is called
+   * dangerouslyGetState is to discourage developers to use internal navigation's state.
+   * Note that this method doesn't re-render screen when the result changes. So don't use it in `render`.
+   */
+  dangerouslyGetState(): State;
 } & EventConsumer<EventMap & EventMapBase> &
   PrivateValueStore<ParamList, RouteName, EventMap>;
 

packages/core/src/useNavigationCache.tsx

@@ -43,19 +43,19 @@ export default function useNavigationCache<
   // Cache object which holds navigation objects for each screen
   // We use `React.useMemo` instead of `React.useRef` coz we want to invalidate it when deps change
   // In reality, these deps will rarely change, if ever
+  const parentNavigation = React.useContext(NavigationContext);
+
   const cache = React.useMemo(
     () => ({ current: {} as NavigationCache<State, ScreenOptions> }),
     // eslint-disable-next-line react-hooks/exhaustive-deps
-    [getState, navigation, setOptions, router, emitter]
+    [getState, navigation, setOptions, router, emitter, parentNavigation]
   );
 
   const actions = {
     ...router.actionCreators,
     ...BaseActions,
   };
 
-  const parentNavigation = React.useContext(NavigationContext);
-
   cache.current = state.routes.reduce<NavigationCache<State, ScreenOptions>>(
     (acc, route, index) => {
       const previous = cache.current[route.key];
@@ -92,6 +92,7 @@ export default function useNavigationCache<
           ...helpers,
           ...emitter.create(route.key),
           dangerouslyGetParent: () => parentNavigation,
+          dangerouslyGetState: getState as () => State,
           dispatch,
           setOptions: (options: object) =>
             setOptions(o => ({