Time delta between websocket messages

Client.js

var client = new WebSocket("ws://IP:1337");

var last = Date.now();

client.addEventListener("message", function(event) {

  var delta = Date.now() - last;

  console.log("Time since last message ", delta, "ms");

  if(delta < 40) console.log("SPIKE");

  last = Date.now();  

});

Server.js

/* Error handler */

function foo() {}

/* List of connected sockets */

var clients = new Set;

/* Server */

var WebSocketServer = require('uws').Server;

var server = new WebSocketServer({
  port: 1337,
  perMessageDeflate: false
});

server.on('connection', function(socket) {

  clients.add(socket);

  socket.on("close", function() {

    clients.delete(this);

  });

});

setInterval(function() {

  var data = "";

  for (var i = 0; i < 1024; i++) data += String.fromCharCode(Math.random() * 128 | 0);

  for (var socket of clients) {

    socket.send(data, {

      compress: false

    }, foo);

  }

}, 1000 / 20);