教學課程：在 Node.js 應用程式中使用變體功能旗標

在本教學課程中，您使用變體功能旗標來管理範例應用程式 Quote of the Day 中不同使用者區段的體驗。您利用使用變體功能旗標中所建立的變體功能旗標。繼續之前，請確定您在應用程式組態存放區中建立名為 Greeting 的變體功能旗標。

先決條件

Node.js的 LTS 版本。
請遵循使用變體功能旗標教學課程，然後建立名為 Greeting 的變體功能旗標。

建立 Node.js 應用程式

建立名為 quote-of-the-day 的資料夾，並初始化專案。
```
mkdir quote-of-the-day
cd quote-of-the-day
npm init -y
```

安裝下列套件。

npm install @azure/app-configuration-provider
npm install @microsoft/feature-management
npm install express

建立名為 server.js 的新檔案，並新增下列程序代碼。

const express = require("express");
const server = express();

const appConfigEndpoint = process.env.AZURE_APPCONFIG_ENDPOINT;
const { DefaultAzureCredential } = require("@azure/identity");
const { load } = require("@azure/app-configuration-provider");
const { FeatureManager, ConfigurationMapFeatureFlagProvider } = require("@microsoft/feature-management");

let appConfig;
let featureManager;

async function initializeConfig() {
    appConfig = await load(appConfigEndpoint, new DefaultAzureCredential(), {
        featureFlagOptions: {
            enabled: true,
            refresh: {
                enabled: true
            }
        }
    });

    featureManager = new FeatureManager(
        new ConfigurationMapFeatureFlagProvider(appConfig));
}

function startServer() {
    // Use a middleware to refresh the configuration before each request
    server.use((req, res, next) => {
        appConfig.refresh();
        next();
    });
    server.use(express.json());
    // Serve static index.html from the current folder
    server.use(express.static("."));

    // This API returns the different greeting messages based on the segment the user belongs to.
    // It evaluates a variant feature flag based on user context. The greeting message is retrieved from the variant configuration.
    server.get("/api/getGreetingMessage", async (req, res) => {
        const { userId, groups } = req.query;
        const variant = await featureManager.getVariant("Greeting", { userId: userId, groups: groups ? groups.split(",") : [] });
        res.status(200).send({ message: variant?.configuration });
    });

    server.post("/api/like", (req, res) => {
        const { UserId } = req.body;
        if (UserId === undefined) {
            return res.status(400).send({ error: "UserId is required" });
        }
        // Here you would typically emit a 'like' event to compare variants.
        res.status(200).send();
    });

    const port = "8080";
    server.listen(port, () => {
        console.log(`Server is running at http://localhost:${port}`);
    });
}

// Initialize the configuration and start the server
initializeConfig()
    .then(() => {
        startServer();
    })
    .catch((error) => {
        console.error("Failed to load configuration:", error);
        process.exit(1);
    });

建立名為 index.html 的新檔案，並新增下列程序代碼：

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Quote of the Day</title>
<style>
    .heart-button {
    background-color: transparent;
    border: none;
    cursor: pointer;
    font-size: 24px;
    }

    .heart-button:hover {
    background-color: #F0F0F0;
    }
</style>
</head>
<body>
<div style="display: flex; flex-direction: column; min-height: 100vh; background-color: #f4f4f4;">
    <header style="background-color: white; border-bottom: 1px solid #eaeaea; display: flex; justify-content: space-between; align-items: center; font-family: 'Arial', sans-serif; font-size: 16px;">
    <div style="font-size: 1.25em; color: black;">QuoteOfTheDay</div>
    </header>

    <main style="display: flex; justify-content: center; align-items: center; flex-grow: 1;">
    <div style="background-color: white; padding: 30px; border-radius: 8px; box-shadow: 0 2px 10px rgba(0, 0, 0, 0.1); max-width: 700px; position: relative; text-align: left;">
        <div id="quote-content">
        <h2 id="greeting">Quote of the Day</h2>
        <blockquote style="font-size: 2em; font-style: italic; color: #4EC2F7; margin: 0 0 20px 0; line-height: 1.4;">
            <p>"You cannot change what you are, only what you do."</p>
            <footer style="font-size: 0.55em; color: black; font-family: 'Arial', sans-serif; font-style: normal; font-weight: bold;">— Philip Pullman</footer>
        </blockquote>
        <div style="position: absolute; top: 10px; right: 10px; display: flex;">
            <button class="heart-button" id="like-button">
            <span id="heart-icon" style="color: #ccc">♥</span>
            </button>
        </div>
        </div>
        <div id="loading" style="display: none;">
        <p>Loading</p>
        </div>
    </div>
    </main>
</div>

<script>
    // extract URL parameters to simulate user login
    document.addEventListener('DOMContentLoaded', function() {
    const urlParams = new URLSearchParams(window.location.search);
    const currentUser = urlParams.get('userId') || '';
    let liked = false;

    const greetingElement = document.getElementById('greeting');
    const heartIcon = document.getElementById('heart-icon');
    const likeButton = document.getElementById('like-button');
    const quoteContent = document.getElementById('quote-content');
    const loadingElement = document.getElementById('loading');

    async function init() {
        quoteContent.style.display = 'none';
        loadingElement.style.display = 'block';

        const response = await fetch(`/api/getGreetingMessage?userId=${currentUser}`, { 
        method: "GET"
        });
        const result = await response.json();
        greetingElement.textContent = result.message || "";
        quoteContent.style.display = 'block';
        loadingElement.style.display = 'none';
    }

    likeButton.addEventListener('click', async function() {
        if (!liked) {
        const response = await fetch("/api/like", { 
            method: "POST", 
            headers: { "Content-Type": "application/json" },
            body: JSON.stringify({ UserId: currentUser }),
        });
        }
        liked = !liked;
        heartIcon.style.color = liked ? 'red' : '#ccc';
    });

    init();
    });
</script>
</body>
</html>

為了簡化，此範例會從URL查詢參數中提取userId，例如?userId=UserA，以模擬不同的使用者身分識別。

執行應用程式

將名為 AZURE_APPCONFIG_ENDPOINT 的環境變數設定為在 Azure 入口網站中，於市集的總覽底下找到的應用程式組態存放區端點。

如果您使用 Windows 命令提示字元，請執行下列命令，然後重新啟動命令提示字元以讓變更生效：
```
setx AZURE_APPCONFIG_ENDPOINT "<endpoint-of-your-app-configuration-store>"
```
如果您使用 PowerShell，請執行下列命令：
```
$Env:AZURE_APPCONFIG_ENDPOINT = "<endpoint-of-your-app-configuration-store>"
```
如果您使用 macOS 或 Linux，請執行下列命令：
```
export AZURE_APPCONFIG_ENDPOINT='<endpoint-of-your-app-configuration-store>'
```
執行應用程式。
```
node server.js
```
請開啟瀏覽器，然後瀏覽至 localhost:8080。您應該會看到沒有任何問候訊息之應用程式的默認檢視。
您可以使用 userId 網址中的查詢參數來指定使用者識別碼。流覽 localhost:8080/?userId=UserA 並看到長問候語訊息。
請嘗試不同的使用者識別碼，以查看變體功能旗標如何變更不同使用者區段的問候訊息。流覽 localhost:8080/?userId=UserB 並看到較短的問候訊息。