add back end code

server.js

@@ -0,0 +1,33 @@
+// server.js
+const express = require('express');
+const mysql = require('mysql2/promise');
+const cors = require('cors');
+const multer = require('multer');
+const xlsx = require('xlsx');
+const app = express();
+
+// 数据库配置
+const dbConfig = {
+  host: 'your_host',
+  user: 'your_user',
+  password: 'your_password',
+  database: 'attendance_system'
+};
+
+// 中间件
+app.use(cors());
+app.use(express.json());
+const upload = multer({ dest: 'uploads/' }); // 用于处理Excel上传
+
+// 连接数据库
+let db;
+async function connectDB() {
+  db = await mysql.createConnection(dbConfig);
+  console.log('数据库连接成功');
+}
+connectDB();
+
+// 启动服务
+app.listen(3000, () => {
+  console.log('后端服务运行在 http://localhost:3000');
+});