[react-native] Add a basic sample for AppConfiguration (Azure#21907)

* [react-native] Add a basic sample for AppConfiguration

* Apply suggestions from code review

Co-authored-by: Harsha Nalluru <sanallur@microsoft.com>

Co-authored-by: Harsha Nalluru <sanallur@microsoft.com>

samples/frameworks/react-native-expo/ts/appconfigBasic/.gitignore

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+node_modules/
+.expo/
+dist/
+npm-debug.*
+*.jks
+*.p8
+*.p12
+*.key
+*.mobileprovision
+*.orig.*
+web-build/
+.env
+
+# macOS
+.DS_Store

samples/frameworks/react-native-expo/ts/appconfigBasic/App.tsx

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+import { StatusBar } from 'expo-status-bar';
+import { Button, StyleSheet, Text, View } from 'react-native';
+
+import "./shims";
+import { runAppConfigSample } from "./appConfigSample";
+
+export default function App() {
+  return (
+    <View style={styles.container}>
+      <Text>Open up App.tsx to start working on your app!</Text>
+      <Button title="Click me!" onPress={() => runAppConfigSample() } />
+      <StatusBar style="auto" />
+    </View>
+  );
+}
+
+const styles = StyleSheet.create({
+  container: {
+    flex: 1,
+    backgroundColor: '#fff',
+    alignItems: 'center',
+    justifyContent: 'center',
+  },
+});

samples/frameworks/react-native-expo/ts/appconfigBasic/README.md

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+# Azure SDK samples for React Native using Expo (TypeScript)
+
+This sample application shows how to use the TypeScript client libraries for Azure in some common scenarios.
+
+In this sample, we build a simple application in React Native using Expo and integrating with Azure App Configuration service.
+
+## Prerequisites
+
+The samples are compatible with [LTS versions of Node.js](https://nodejs.org/about/releases/).
+
+Before running the samples in Node, they must be compiled to JavaScript using the TypeScript compiler. For more information on TypeScript, see the [TypeScript documentation][typescript].
+
+The sample is using [Expo](https://expo.dev/), a framework and platform for universal React applications.
+
+You need [an Azure subscription][freesub] and the following resources created to run this sample:
+
+## Step by step
+
+### Create the project
+
+Run expo CLI to create a blank project with typescript support, give it a name of `appconf-rn-expo`.
+
+```shell
+expo init -t expo-template-blank-typescript
+```
+
+At this point, we should be able to see the app running if the environment is set up correctly
+
+```shell
+expo start --android
+```
+
+### Add a button to the app
+
+Open App.tsx and add the following code so it looks similar to following code
+```diff
+-import { StyleSheet, Text, View } from 'react-native';
++import { Button, StyleSheet, Text, View } from 'react-native';
++import { runAppConfigSample } from "./appConfigSample";
+...
+
+      <Text>Open up App.tsx to start working on your app!</Text>
++     <Button title="Click me!" onPress={() => runAppConfigSample() } />
+      <StatusBar style="auto" />
+```
+
+### Add the App Configuration sample file
+
+create a new file `appConfigSample.ts` in the sample directory as `App.tsx` with following content from [appConfigSample.ts](./appConfigSample.ts) file
+
+### Add dependencies
+
+We need to add a dependency to the JavaScript Client SDK library for Azure App Configuration (version 1.4.0-beta.1 or later). We use `@babel/plugin-proposal-async-generator-functions` to help transform async iterator usage in our sample. We also use `babel-plugin-inline-dotenv` to help load secrets from our `.env` file while developing.
+
+```shell
+yarn add @azure/app-configuration@1.4.0-beta.1
+yarn add --dev babel-plugin-inline-dotenv @babel/plugin-proposal-async-generator-functions
+```
+
+Then add the following into `babel.config.js` to enable the plugin
+
+```diff
+    presets: ["babel-preset-expo"],
++    plugins: [
++      "@babel/plugin-proposal-async-generator-functions",
++      ["inline-dotenv", { unsafe: true }],
++    ],
+```
+
+### Add connection string to .env file
+
+Create a `.env` file in the project directory. Retrieve your connection string from Azure portal and add them to the `.env` file. Since this file contains secrets you need to add it to the ignore list if your code is committed to a repository.
+
+**Note** We use connection string directly here for testing purpose.  You should consider the trade-off between security and convenience and better use a backend to dynamically provide secrets to only authenticated users.
+
+```
+APPCONFIG_CONNECTION_STRING="<your app configuration connection string>"
+```
+
+**Note**: if you update the .env file, you would need to clear expo cache and rebuild. It can be done by passing `-c` to the start command, for example, in `package.json`
+
+```diff
+-    "android": "expo start --android",
++    "android": "expo start --android -c",
+```
+
+### Add polyfills
+
+The `crypto` dependency of the JavaScript Client SDK library for Azure App Configuration are not available in React-Native, so we need to provide polyfills for them. We also need to polyfill the `TextEncoder` API. Add the following dependencies to the project
+
+```shell
+yarn add isomorphic-webcrypto react-native-get-random-values react-native-url-polyfill text-encoding-polyfill
+```
+
+Then add a `shims.ts` file in the project root with the following content
+
+```typescript
+import 'react-native-url-polyfill/auto';
+import "react-native-get-random-values";
+import "text-encoding-polyfill";
+const getRandomValues = global.crypto.getRandomValues;
+import * as crypto from "isomorphic-webcrypto";
+global.crypto = crypto;
+global.crypto.getRandomValues = getRandomValues;
+```
+
+Then add the following line to `App.tsx`
+
+```diff
++import "./shims";
+import { runAppConfigSample } from "./appConfigSample";
+```
+
+Now run the app in the emulator (Android in this case)
+
+```shell
+npm run android
+```
+
+Click on the **CLICK ME!** button, you should see the following logged to the console output!
+
+```
+Running helloworld sample
+Adding in new setting Samples:Greeting
+Samples:Greeting has been set to Hello!
+Samples:Greeting has been set to Goodbye!
+Samples:Greeting has been deleted
+```

samples/frameworks/react-native-expo/ts/appconfigBasic/app.json

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+{
+  "expo": {
+    "name": "appconf-rn-expo",
+    "slug": "appconf-rn-expo",
+    "version": "1.0.0",
+    "orientation": "portrait",
+    "icon": "./assets/icon.png",
+    "splash": {
+      "image": "./assets/splash.png",
+      "resizeMode": "contain",
+      "backgroundColor": "#ffffff"
+    },
+    "updates": {
+      "fallbackToCacheTimeout": 0
+    },
+    "assetBundlePatterns": [
+      "**/*"
+    ],
+    "ios": {
+      "supportsTablet": true
+    },
+    "android": {
+      "adaptiveIcon": {
+        "foregroundImage": "./assets/adaptive-icon.png",
+        "backgroundColor": "#FFFFFF"
+      }
+    },
+    "web": {
+      "favicon": "./assets/favicon.png"
+    }
+  }
+}

samples/frameworks/react-native-expo/ts/appconfigBasic/appConfigSample.ts

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+/**
+ * @summary Demonstrates the CRUD operations on the configuration settings.
+ */
+import { AppConfigurationClient } from "@azure/app-configuration";
+
+export async function runAppConfigSample() {
+  console.log(`Running helloworld sample`);
+
+  // Set the following environment variable or edit the value on the following line.
+  const connectionString =
+    process.env["APPCONFIG_CONNECTION_STRING"] || "<connection string>";
+  const client = new AppConfigurationClient(connectionString);
+
+  const greetingKey = "Samples:Greeting";
+
+  await cleanupSampleValues([greetingKey], client);
+
+  // creating a new setting
+  console.log(`Adding in new setting ${greetingKey}`);
+  await client.addConfigurationSetting({ key: greetingKey, value: "Hello!" });
+
+  const newSetting = await client.getConfigurationSetting({ key: greetingKey });
+  console.log(`${greetingKey} has been set to ${newSetting.value}`);
+
+  // changing the value of a setting
+  await client.setConfigurationSetting({ key: greetingKey, value: "Goodbye!" });
+
+  const updatedSetting = await client.getConfigurationSetting({
+    key: greetingKey,
+  });
+  console.log(`${greetingKey} has been set to ${updatedSetting.value}`);
+
+  // removing the setting
+  await client.deleteConfigurationSetting({ key: greetingKey });
+  console.log(`${greetingKey} has been deleted`);
+
+  await cleanupSampleValues([greetingKey], client);
+}
+
+async function cleanupSampleValues(
+  keys: string[],
+  client: AppConfigurationClient
+) {
+  const settingsIterator = client.listConfigurationSettings({
+    keyFilter: keys.join(","),
+  });
+
+  for await (const setting of settingsIterator) {
+    await client.deleteConfigurationSetting({
+      key: setting.key,
+      label: setting.label,
+    });
+  }
+}

samples/frameworks/react-native-expo/ts/appconfigBasic/babel.config.js

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+module.exports = function(api) {
+  api.cache(true);
+  return {
+    presets: ["babel-preset-expo"],
+    plugins: [
+      "@babel/plugin-proposal-async-generator-functions",
+      ["inline-dotenv", { unsafe: true }],
+    ],
+  };
+};

samples/frameworks/react-native-expo/ts/appconfigBasic/package.json

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+{
+  "name": "appconf-rn-expo",
+  "version": "1.0.0",
+  "main": "node_modules/expo/AppEntry.js",
+  "scripts": {
+    "start": "expo start",
+    "android": "expo start --android",
+    "ios": "expo start --ios",
+    "web": "expo start --web",
+    "eject": "expo eject"
+  },
+  "dependencies": {
+    "@azure/app-configuration": "1.4.0-beta.1",
+    "expo": "~44.0.0",
+    "expo-status-bar": "~1.2.0",
+    "isomorphic-webcrypto": "^2.3.8",
+    "react": "17.0.1",
+    "react-dom": "17.0.1",
+    "react-native": "0.64.3",
+    "react-native-get-random-values": "^1.7.2",
+    "react-native-url-polyfill": "^1.3.0",
+    "react-native-web": "0.17.1",
+    "text-encoding-polyfill": "^0.6.7"
+  },
+  "devDependencies": {
+    "@babel/core": "^7.12.9",
+    "@babel/plugin-proposal-async-generator-functions": "^7.16.8",
+    "@types/react": "~17.0.21",
+    "@types/react-native": "~0.64.12",
+    "babel-plugin-inline-dotenv": "^1.7.0",
+    "typescript": "~4.3.5"
+  },
+  "private": true
+}

samples/frameworks/react-native-expo/ts/appconfigBasic/shims.ts

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+import 'react-native-url-polyfill/auto';
+import "react-native-get-random-values";
+import "text-encoding-polyfill";
+const getRandomValues = global.crypto.getRandomValues;
+import * as crypto from "isomorphic-webcrypto";
+global.crypto = crypto;
+global.crypto.getRandomValues = getRandomValues;

samples/frameworks/react-native-expo/ts/appconfigBasic/tsconfig.json

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+{
+  "extends": "expo/tsconfig.base",
+  "compilerOptions": {
+    "strict": true
+  }
+}