ws-client.js

const WebSocket = require('ws');

const ws = new WebSocket('wss://127.0.0.1');

ws.on('open', function open() {
  ws.send('something');
});

ws.on('message', function incoming(data) {
  console.log(data);
});

ws-server.js

const WebSocket = require('ws');

const wss = new WebSocket.Server({ port: 8080 });

wss.on('connection', function connection(ws) {
  ws.on('message', function incoming(message) {
    console.log('received: %s', message);
  });

  ws.send('something');
});