const WebSocket = require('ws');

const wsServer = new WebSocket.Server({port: 9000});

// socket connect
wsServer.on('connection', (socket) => {

     var a = "";

     // socket close
     socket.on('message', (message) =>
     {

     });

     // socket close
     socket.on('close', () =>
     {

     });

});

<script>
     var socket = new WebSocket("ws://localhost:9000");
</script>