Initial backend setup with Express and Socket.IO

.env.example

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+PORT=5000
+NODE_ENV=development
+CORS_ORIGIN=http://localhost:3000

.gitignore

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+node_modules/
+.env
+.DS_Store
+*.log

package.json

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+{
+  "name": "dashboard-backend",
+  "version": "1.0.0",
+  "description": "Real-time cryptocurrency dashboard backend",
+  "main": "server.js",
+  "scripts": {
+    "start": "node server.js",
+    "dev": "nodemon server.js"
+  },
+  "keywords": [
+    "express",
+    "socket.io",
+    "realtime",
+    "crypto"
+  ],
+  "author": "CloudForge",
+  "license": "ISC",
+  "dependencies": {
+    "axios": "^1.13.1",
+    "cors": "^2.8.5",
+    "dotenv": "^17.2.3",
+    "express": "^5.1.0",
+    "socket.io": "^4.8.1"
+  },
+  "devDependencies": {
+    "nodemon": "^3.1.10"
+  }
+}

server.js

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+const express = require("express");
+const http = require("http");
+const socketIo = require("socket.io");
+const cors = require("cors");
+const axios = require("axios");
+require("dotenv").config();
+
+const app = express();
+
+const server = http.createServer(app);
+
+const io = socketIo(server, {
+  cors: {
+    origin: process.env.CORS_ORIGIN || "*",
+    methods: ["GET", "POST"],
+  },
+});
+
+// ========== (Middleware) ==========
+
+app.use(cors());
+
+app.use(express.json());
+
+// ========== HTTP Route ==========
+
+app.get("/health", (req, res) => {
+  res.json({
+    status: "OK",
+    message: "Server is running",
+    timestamp: new Date().toISOString(),
+  });
+});
+
+// ========== Socket.IO Logic ==========
+
+// 用於追蹤連接的客戶端數量
+let connectedClients = 0;
+
+// 當客戶端連接時觸發
+io.on("connection", (socket) => {
+  // 增加客戶端計數
+  connectedClients++;
+
+  console.log(`✅ 客戶端已連接: ${socket.id}`);
+  console.log(`📊 當前連接數: ${connectedClients}`);
+
+  // 向所有客戶端廣播當前連接數
+  io.emit("clientCount", connectedClients);
+
+  // ========== 監聽客戶端事件 ==========
+
+  // 當客戶端要求數據時
+  socket.on("requestData", async (dataType) => {
+    console.log(`📤 數據請求: ${dataType}`);
+
+    try {
+      let data;
+
+      if (dataType === "crypto") {
+        // 從 CoinGecko API 獲取加密貨幣數據
+        const response = await axios.get(
+          "https://api.coingecko.com/api/v3/simple/price",
+          {
+            params: {
+              // 要查詢的加密貨幣
+              ids: "bitcoin,ethereum,cardano,solana,ripple",
+              // 使用 USD 幣種
+              vs_currencies: "usd",
+              // 包含市值
+              include_market_cap: true,
+              // 包含24小時交易量
+              include_24hr_vol: true,
+              // 包含24小時漲跌幅
+              include_24hr_change: true,
+            },
+          }
+        );
+
+        // 組織數據格式
+        data = {
+          type: "crypto",
+          timestamp: new Date(),
+          prices: response.data,
+        };
+      }
+
+      // 發送數據給要求的客戶端
+      socket.emit("data", data);
+      console.log(`✅ 數據已發送給客戶端: ${socket.id}`);
+    } catch (error) {
+      console.error("❌ 獲取數據出錯:", error.message);
+      // 發送錯誤信息給客戶端
+      socket.emit("error", {
+        message: "Failed to fetch data",
+        details: error.message,
+      });
+    }
+  });
+
+  // ========== 定期推送數據 ==========
+
+  // 創建定時器，每5秒推送一次數據給該客戶端
+  const dataInterval = setInterval(async () => {
+    try {
+      // 獲取最新的加密貨幣數據
+      const response = await axios.get(
+        "https://api.coingecko.com/api/v3/simple/price",
+        {
+          params: {
+            ids: "bitcoin,ethereum,cardano,solana,ripple",
+            vs_currencies: "usd",
+            include_market_cap: true,
+            include_24hr_vol: true,
+            include_24hr_change: true,
+          },
+        }
+      );
+
+      // 向該客戶端發送數據（實時更新）
+      socket.emit("data", {
+        type: "crypto",
+        timestamp: new Date(),
+        prices: response.data,
+      });
+    } catch (error) {
+      console.error("❌ 定時推送出錯:", error.message);
+    }
+  }, 5000); // 每5000毫秒（5秒）執行一次
+
+  // ========== 客戶端斷開連接 ==========
+
+  // 當客戶端斷開連接時觸發
+  socket.on("disconnect", () => {
+    connectedClients--;
+    console.log(`❌ 客戶端已斷開: ${socket.id}`);
+    console.log(`📊 當前連接數: ${connectedClients}`);
+
+    // 向所有客戶端廣播更新的連接數
+    io.emit("clientCount", connectedClients);
+
+    // 清除該客戶端的定時器
+    clearInterval(dataInterval);
+  });
+});
+
+// ========== 啟動服務器 ==========
+
+// 從環境變數獲取端口，或使用默認5000
+const PORT = process.env.PORT || 5000;
+
+// 啟動伺服器
+server.listen(PORT, () => {
+  console.log("");
+  console.log("═══════════════════════════════════════");
+  console.log(`✅ 服務器運行在: http://localhost:${PORT}`);
+  console.log("📡 WebSocket 已準備接收連接");
+  console.log("🔗 CORS 來源:", process.env.CORS_ORIGIN || "*");
+  console.log("═══════════════════════════════════════");
+  console.log("");
+});
+
+// ========== 錯誤處理 ==========
+
+// 處理未捕獲的異常
+process.on("unhandledRejection", (err) => {
+  console.error("❌ 未捕獲的異常:", err);
+});
+
+process.on("uncaughtException", (err) => {
+  console.error("❌ 未捕獲的異常:", err);
+  process.exit(1);
+});