"解决了"
只是我生成一个数字分配给每个客户端（可以是不同的设备之间的对方），我发送随机数生成的服务器到每个连接！

在“* 连接 *”之前，应添加：

const WS = require('ws');
const WS_PORT = 8081
const express = require('express');
const app = express();
const PORT = 3000;

app.listen(PORT, () => console.log(`Server listening , go to http://localhost:${PORT}`));
app.use(express.static('public'));

const wss = new WS.Server({ port: WS_PORT })

const wsSelected = new Set();
// Creating connection using websocket

const interval = setInterval(() => {
    const randomNumber = Math.floor(Math.random() * 100);
    //Sending same number to each client
    wsSelected.forEach(ws => 
        ws.send(randomNumber)
    )
}, 2000);

在“* 连接 *”之后，您应该添加：

wss.on("connection", ws => {
    console.log("New client!");

    //This line you should add
    wsSelected.add(ws);

    ...