Question

Can javascript access the system ports ?
If yes, is it possible to write a server (TCP/UDP in C) to which data can be send from javascript ?

Answer 1

Let’s assume that you’re not asking for Node.js.

You can write WebSocket server in C and connect your JavaScript to it. There are already plenty of implementations so you don’t have to write it yourself.

When you start your server and bind it to specific host name and port you can connect from your JavaScript by:

var ws = new WebSocket('ws://hostname:port');
ws.onopen = function () {
   console.log('Connected');
};
ws.onmessage = function () {
   console.log('New message...');
};
ws.send('Some message...');

For example, here is one http://code.google.com/p/cwebsocket/.

As far as I know WebSocket is over TCP.

One more option is to create HTTP server use AJAX with or without long polling.