检测客户端是否使用socket.io(NodeJs)与网络断开连接

我正在创建一个带有node.js和socket.io的应用程序。我需要检测客户端是否已断开与internet的连接,并手动/自动启动socket.disconnect()。

我已经找了,但找不到任何解决办法。

const app = require('express')();
const server = require('http').Server(app);
const io = require('socket.io')(server);
const fs = require('fs');

server.listen(8005, () => console.log('app is running at 8005 port'));

app.get('/', (req, res) => {
    res.sendFile(__dirname + '/index.html');
})

const sockets = {};
io.sockets.on('connection', (socket) => {
    socket.once('disconnect', function () {
        console.log('-------disconencted', socket.userId); 
        delete sockets[socket.userId];
    });
    socket.on('init', (data) => {
        socket.userId = data.userId;
        sockets[data.userId] = socket;
        sockets[data.userId].emit('userOnline', { id : data.userId});
        console.log(socket.userId,'--------useronline-----------',data)
    });


    socket.on('test', (data) => {
        socket.emit('testResp', { id : 'sdfd'});
        console.log('--------useronline-----------',socket.userId);
    });

    socket.on('total', data => {
        socket.emit('totalResp', { users: Object.keys(sockets)})
        console.log('--------total-----------',socket.userId);

    })





})

客户端代码:

var socket = io('http://localhost:8005');
    socket.on('userOnline', function (data) {
        console.log(socket.userId, '---userOnline--------', data);
    });

    socket.on('testResp', function (data) {
        console.log(socket.userId, '----testResp-------', data);
    });

    socket.on('totalResp', function (data) {
        document.querySelector('#total_users_length').innerHTML = data.users.length;

        console.log(socket.userId, '----totalResp-------', data);
    });
    document.querySelector('#init').addEventListener('click', function(){

        socket.emit('init', {userId: document.querySelector('input').value});
    });

    document.querySelector('#test').addEventListener('click', function(){

      socket.emit('test', {test: 'tst'});
    });

    document.querySelector('#total').addEventListener('click', function(){

    socket.emit('total', {test: 'tst'});
    });

我将用户的用户id存储在socket中,这样当用户断开与服务器的连接时,我可以找到它的id并发送通知。 提前谢谢。