WebSocket简介：

如果要实现服务端主动发送消息到前端，使用axios(基于http)就得被迫轮询，也就是隔一段时间就向服务器发送一次请求。轮询的缺点：效率低、浪费资源（因为必须不停的连接，或者http连接始终打开）。解决这个问题最好的方式就是WebSocket。

安装依赖：

yarn add express express-ws nodemen

package.json

{
  "name": "ws",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "start":"nodemon app.js",
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "dependencies": {
    "express": "^4.18.2",
    "express-ws": "^5.0.2",
    "nodemon": "^2.0.20"
  }
}

//nodemon 保持服务端持续连接实现热更新

Express中间件

app.js

//引入框架
const express= require("express")
const app =express();

//注入express-ws
const expressWs = require("express-ws")
const websocket = require("./websocket.js")
const port = 3000
expressWs(app)
//中间件
app.use("/cat",express.static('public/cat.html'))
app.use("/dog",express.static('public/dog.html'))
app.use('/ws',websocket)
app.use(express.static('public'))

//当服务器找不到页面不做任何操作
app.get("/*",(req,res)=>{})

//监听端口
app.listen(port,()=>{
    console.log(`Server is running at http://localhost:${port}`);
})

WebSocket路由匹配

websocket.js

const express = require("express")
const expressWs = require("express-ws")
const router = express.Router()

expressWs(router)

router.ws("/dog",ws=>{
    //send发射数据
    // ws.send("dog连接成功")
    //接受客户端发来的数据
    ws.on("message",(msg)=>{
        //把数据返回给客户端
        ws.send(msg)
    })
})

module.exports=router

客户端websocket方法

<script>
   //实例化WebSocket 连接服务端
    const ws = new WebSocket("ws://localhost:3000/ws/dog")
    ws.onmessage = function (res) {
        //获取数据
        // console.log(res.data);
        msgbox.innerHTML += rightMsgFn(res.data)
        //添加滚动
        msgbox.scrollTo({
            top: msgbox.scrollHeight,
            behavior: "smooth"
        })
    }
    ws.onopen = function () {
        //值为1代表连接成功
        // console.log(ws.readyState);
    }
    // ws.onmessage = function (res) {
    //     //获取数据
    //     console.log(res.data);
    // }
    ws.onclose = function () {
        console.log('连接已断开');
    }
    ws.onerror = function () {
        console.log('连接错误');
    }
</script>