const io = require('socket.io-client') const port = process.env.PORT || 5000; const socket = io('http://localhost:' + port); let last; function send () { last = new Date(); socket.emit('ping_from_client'); } socket.on('connect', () => { console.log(`connect ${socket.id}`); send(); }); socket.on('disconnect', () => { console.log(`disconnect ${socket.id}`); }); socket.on('pong_from_server', () => { const latency = new Date() - last; console.log('latency is ' + latency + ' ms'); setTimeout(send, 1000); });