const mqtt = require('mqtt');  exports.main = async (event, context) => {   return new Promise((resolve, reject) => {     // 连接到 MQTT 服务器     const client = mqtt.connect('wss://mqtt.example.com:8083/mqtt', {       username: 'your-username',       password: 'your-password',     });      // 连接成功     client.on('connect', () => {       console.log('MQTT 连接成功');       client.subscribe('test/topic', (err) => {         if (err) {           console.error('订阅失败:', err);           reject(err);         } else {           console.log('订阅成功');         }       });     });      // 接收消息     client.on('message', (topic, message) => {       console.log(`收到消息: ${message.toString()}`);       resolve({         topic,         message: message.toString(),       });     });      // 连接失败     client.on('error', (error) => {       console.error('MQTT 连接失败:', error);       reject(error);     });   }); };

注意：  需要用return new Promise((resolve, reject) => { 包起来。我没包起来，导致项目中可用，但是云函数中用不了。