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需求：node做后端根据websocket，连接数据库，数据库的字段改变后，前端不用刷新页面也能更新到数据，前端也可以发送消息给后端，后端接受后把前端消息做处理再推送给前端展示

1.初始化node，生成package.json和package-lock.js

 npm init -y

2.安装express、socket.io、cors

3.创建app.js并编写代码

使用node ./websocket.js运行项目

npm install express socket.io cors -S

建立websocket.js 

const app = require('express')();
const http = require('http').createServer(app);
const io = require('socket.io')(http);
const fs = require('fs');
const cors = require('cors');
// 使用 cors 中间件允许跨域请求
// 配置跨域选项
const corsOptions = {origin: '*', // 指定允许的来源methods: ['GET', 'POST'], // 允许的请求方法credentials: true // 允许发送凭据（如 cookies）
};
app.use(cors(corsOptions));
// 创建数据库连接
const mysql = require('mysql');
const connection = mysql.createConnection({host: 'localhost',//数据库连接域名user: 'root',//数据库账号password: '123456',//密码database: 'graduation_design'//要连接的数据库名
});
connection.connect();// 监听客户端连接事件
io.on('connection', (socket) => {console.log('A client connected');//查询表connection.query('SELECT * FROM shelves', (error, results) => {if (error) throw error;//数据推送到前端socket.emit('data', results);},)// 发送数据到客户端setInterval(() => {// 查询数据库并发送数据到客户端connection.query('SELECT * FROM shelves', (error, results) => {if (error) throw error;socket.emit('data', results);},)}, 60 * 1000);//接收到客户端的消息后再推送给客户端socket.on('message', (message) => {console.log('接收到客户端消息：', message);socket.emit("messagedata", message);})// 监听客户端断开连接事件socket.on('disconnect', () => {console.log('A client disconnected');});
});// 启动服务器
http.listen(3000, () => {console.log('WebSocket server is running on port 3333');
});

4.前端使用socket.io-client

npm install socket.io-client

在需要使用websocket连接的页面引入

<template><div class="content-box"><div class="container">{{ data }}<el-button @click="connectWebscoket">连接websocket</el-button><el-button @click="gasong">发送</el-button><el-button @click="stop">停止连接</el-button><hr />{{ msgdata }}</div></div>
</template><script>
import io from 'socket.io-client'
let socket = null
export default {data() {return {data: null,msgdata: ''}},mounted() {},methods: {connectWebscoket() {// 解决跨域问题socket = io('http://localhost:3333', {transports: ['websocket'],withCredentials: true, //白名单extraHeaders: {//请求头'Access-Control-Allow-Origin': 'http://localhost:8080'}})socket.on('data', (data) => {this.data = data})socket.on('messagedata', (msg) => {this.msgdata = msg})},gasong() {socket.send('Hello from client!')},stop() {socket.close()}}
}
</script><style lang="scss" scoped></style>

 此时已经建立好websocket的连接