NodeJS server not accessible from outside

I think you should try not specifying an IP.

var http = require('http');
http.createServer(function (req, res) {
  res.writeHead(200, {'Content-Type': 'text/plain'});
  res.end('Simple server\n');
}).listen(8080);
console.log('Server running at http://0.0.0.0:8080/');

I am pretty sure that you have to use

iptables -A OUTPUT -p tcp  --sport 8080 -j ACCEPT

for the outgoing rule (not dport). Apart from that, maybe there's an earlier rule that blocks the traffic? Try iptables -L.