feat(react): allow custom feature app rendering

This deprecates the `renderError` prop.

fixes #296
fixes #295

docs/guides/integrating-the-feature-hub.md

@@ -318,6 +318,15 @@ be provided:
 For more details please refer to the the
 ["Feature App Configs" section](#feature-app-configs).
 
+#### `children`
+
+One can pass a rendering function as the React Children (i.e. the `children`
+prop) that allows custom rendering of the Feature App during loading and error
+states.
+
+For more details please refer to the the
+["Custom Loading and Error UI" section](#custom-loading-and-error-ui).
+
 ### React Feature App Container
 
 The `FeatureAppContainer` component allows the integrator to bundle Feature Apps
@@ -395,6 +404,15 @@ be provided:
 For more details please refer to the the
 ["Feature App Configs" section](#feature-app-configs).
 
+#### `children`
+
+One can pass a rendering function as the React Children (i.e. the `children`
+prop) that allows custom rendering of the Feature App during loading and error
+states.
+
+For more details please refer to the the
+["Custom Loading and Error UI" section](#custom-loading-and-error-ui).
+
 ### Error Handling
 
 When a Feature App throws an error while rendering or, in the case of a
@@ -403,6 +421,63 @@ When a Feature App throws an error while rendering or, in the case of a
 however, rendering errors are not caught and must therefore be handled by the
 integrator.
 
+### Custom Loading and Error UI
+
+An integrator can customize the rendering of Loading states and Errors, using
+the `children` "render prop" in `FeatureAppContainer` or `FeatureAppLoader`.
+
+The `children` prop is a function that receives parameters in form of an object
+and returns rendered React children (a React Node).
+
+Please [look at the API reference][custom-rendering-param-api], to learn more
+about the passed params:
+
+- [`error`][custom-rendering-param-error-api]
+- [`loading`][custom-rendering-param-loading-api]
+- [`featureAppNode`][custom-rendering-param-featureappnode-api]
+
+> This API allows full control over the rendering output, and must therefore
+> abide a set of rules that need to be followed carefully:
+>
+> - **The `featureAppNode` might be passed and has to be rendered, even when
+>   `loading=true`.**  
+>   A Feature App might depend on being rendered, before resolving its loading
+>   promise. To not show the Feature App in favour of a loading UI, it must be
+>   **hidden visually** (e.g. via `display: none;`).
+> - **The `featureAppNode` should always be rendered into the same position of
+>   the returned tree.**  
+>   Otherwise it could occur, that React re-mounts the Feature App, which is
+>   resource-expensive and can break DOM Feature Apps.
+
+#### Custom UI Example
+
+> The following example can also be seen with more context in the ["React
+> Loading UI"][react-loading-ui-demo] and ["React Error
+> Handling"][react-error-handling-demo] demos.
+
+```jsx
+<FeatureAppContainer
+  featureAppId="some-feature-app"
+  featureAppDefinition={someFeatureAppDefinition}
+  //...
+>
+  {({ error, loading, featureAppNode }) => {
+    if (error) {
+      return <ErrorUi error={error}>
+    }
+
+    return (
+      <div>
+        <div style={{display: loading ? 'none' : 'initial'}}>
+          {featureAppNode}
+        </div>
+        {loading && <Spinner />}
+      </div>
+    );
+  }}
+</FeatureAppContainer>
+```
+
 ## Placing Feature Apps on a Web Page Using Web Components
 
 An integrator can use the `feature-app-loader` or the `feature-app-container`
@@ -743,3 +818,15 @@ someFeatureService2.foo(42);
 [own-feature-service-definitions]:
   /docs/guides/writing-a-feature-app#ownfeatureservicedefinitions
 [sharing-npm-dependencies]: /docs/guides/sharing-npm-dependencies
+[custom-rendering-param-api]:
+  /@feature-hub/interfaces/react.customfeatureapprenderingparams.html
+[custom-rendering-param-error-api]:
+  /@feature-hub/interfaces/react.customfeatureapprenderingparams.html#error
+[custom-rendering-param-loading-api]:
+  /@feature-hub/interfaces/react.customfeatureapprenderingparams.html#loading
+[custom-rendering-param-featureappnode-api]:
+  /@feature-hub/interfaces/react.customfeatureapprenderingparams.html#featureappnode
+[react-loading-ui-demo]:
+  https://github.com/sinnerschrader/feature-hub/tree/master/packages/demos/src/react-loading-ui
+[react-error-handling-demo]:
+  https://github.com/sinnerschrader/feature-hub/tree/master/packages/demos/src/react-error-handling

docs/guides/writing-a-feature-app.md

@@ -222,6 +222,48 @@ const myFeatureAppDefinition = {
 };
 ```
 
+### Loading UIs provided by the React Integrator
+
+Both kinds of Feature Apps can specify a loading stage for Feature Apps, which
+are used to allow an Integrator to hide an already rendered Feature App visually
+and display a custom loading UI instead. This feature is for client-side
+rendering only.
+
+A Feature App can declare this loading stage by passing a `Promise` in the
+object returned from their `create` function with the key `loadingPromise`. Once
+the promise resolves, the loading is considered done. If it rejects, the Feature
+App will be considered as crashed, and the Integrator can use the rejection
+payload to display a custom Error UI.
+
+```js
+const myFeatureAppDefinition = {
+  create(env) {
+    const dataPromise = fetchDataFromAPI();
+
+    return {
+      loadingPromise: dataPromise,
+
+      render() {
+        return <App dataPromise={dataPromise}>;
+      }
+    };
+  }
+};
+```
+
+> **Note:**  
+> If you want the rendered App to control when it is done loading, you can pass
+> the promise `resolve` and `reject` functions into the App using your render
+> method. An example for this is implemented in the [`react-loading-ui`
+> demo][demo-react-loading-ui].
+
+> **Note:**  
+> If a similar loading stage (after rendering started) is needed for server-side
+> rendering, for example to wait for a data layer like a router to resolve all
+> dependencies, it can be implemented using the
+> [`@feature-hub/async-ssr-manager`][async-ssr-manager-api]'s `scheduleRerender`
+> API.
+
 ## Implementing a Feature App for an Integrator That Uses Web Components
 
 If the targeted integrator is using the [`@feature-hub/dom`][dom-api] package, a
@@ -272,3 +314,6 @@ const myFeatureAppDefinition = {
 [issue-245]: https://github.com/sinnerschrader/feature-hub/issues/245
 [providing-a-versioned-api]:
   /docs/guides/writing-a-feature-service#providing-a-versioned-api
+[async-ssr-manager-api]: /@feature-hub/modules/async_ssr_manager.html
+[demo-react-loading-ui]:
+  https://github.com/sinnerschrader/feature-hub/tree/master/packages/demos/src/react-loading-ui

packages/demos/src/react-loading-and-error-ui/feature-app.tsx

@@ -0,0 +1,69 @@
+import {Text} from '@blueprintjs/core';
+import {FeatureAppDefinition} from '@feature-hub/core';
+import {ReactFeatureApp} from '@feature-hub/react';
+import * as React from 'react';
+
+const getFakeServerLag = async (ms: number) =>
+  new Promise(resolve => setTimeout(resolve, ms));
+
+async function fetchDataFromServer(): Promise<string> {
+  await getFakeServerLag(3000);
+
+  if (Math.random() > 0.5) {
+    throw Error(`Server Error: Bad luck!
+For performance reasons this server flips a coin to consider which calls to answer.
+Reload the demo to try again.`);
+  }
+
+  return 'You got lucky! Have some juicy server data. Reload the example for a chance at an error.';
+}
+
+interface AppProps {
+  loadingDone: () => void;
+  loadingError: (err: Error) => void;
+}
+
+const App: React.FunctionComponent<AppProps> = ({
+  loadingDone,
+  loadingError
+}) => {
+  const [serverResponse, setServerResponse] = React.useState<string | null>(
+    null
+  );
+
+  React.useEffect(() => {
+    fetchDataFromServer()
+      .then(setServerResponse)
+      .then(loadingDone)
+      .catch(loadingError);
+  }, [loadingDone, loadingError]);
+
+  if (!serverResponse) {
+    return null;
+  }
+
+  return (
+    <Text>
+      <span>The feature app is ready to display, after server responded:</span>
+      <pre>{serverResponse}</pre>
+    </Text>
+  );
+};
+
+const featureAppDefinition: FeatureAppDefinition<ReactFeatureApp> = {
+  create: () => {
+    let resolve: () => void;
+    let reject: (err: Error) => void;
+
+    const loadingPromise: Promise<void> = new Promise(
+      (res, rej) => ([resolve, reject] = [res, rej])
+    );
+
+    return {
+      loadingPromise,
+      render: () => <App loadingDone={resolve} loadingError={reject} />
+    };
+  }
+};
+
+export default featureAppDefinition;

packages/demos/src/react-loading-and-error-ui/integrator.tsx

@@ -0,0 +1,56 @@
+import {Callout, Card, H4, Intent, Spinner} from '@blueprintjs/core';
+import {createFeatureHub} from '@feature-hub/core';
+import {defineExternals, loadAmdModule} from '@feature-hub/module-loader-amd';
+import {FeatureAppLoader, FeatureHubContextProvider} from '@feature-hub/react';
+import * as React from 'react';
+import * as ReactDOM from 'react-dom';
+import '../blueprint-css';
+
+defineExternals({react: React});
+
+const {featureAppManager} = createFeatureHub('test:integrator', {
+  moduleLoader: loadAmdModule,
+  providedExternals: {react: process.env.REACT_VERSION as string}
+});
+
+function ErrorUi({error}: {error: Error}): JSX.Element {
+  return (
+    <Callout intent={Intent.DANGER}>
+      <H4>Example Error UI</H4>
+      <p>{error.message}</p>
+    </Callout>
+  );
+}
+
+ReactDOM.render(
+  <div style={{padding: '20px'}}>
+    <FeatureHubContextProvider value={{featureAppManager}}>
+      <FeatureAppLoader
+        featureAppId="test:invalid"
+        src="feature-app.umd.js"
+        onError={console.warn}
+      >
+        {({error, featureAppNode, loading}) => {
+          if (error) {
+            return <ErrorUi error={error} />;
+          }
+
+          return (
+            <Card>
+              <div style={{display: loading ? 'none' : 'initial'}}>
+                {featureAppNode}
+              </div>
+              {loading && (
+                <div>
+                  <Spinner />
+                  Example Loading UI…
+                </div>
+              )}
+            </Card>
+          );
+        }}
+      </FeatureAppLoader>
+    </FeatureHubContextProvider>
+  </div>,
+  document.querySelector('main')
+);

packages/demos/src/react-error-handling/webpack-config.js → packages/demos/src/react-loading-and-error-ui/webpack-config.js

@@ -9,7 +9,7 @@ const webpackBaseConfig = require('../webpack-base-config');
  */
 const configs = [
   merge.smart(webpackBaseConfig, {
-    entry: path.join(__dirname, './feature-app.ts'),
+    entry: path.join(__dirname, './feature-app.tsx'),
     externals: {
       react: 'react'
     },