How to connect 5 publishers with 5 subscribers over TCP using ZeroMQ's XPUB/XSUB proxy

xpub-xsub.js

// How to connect 5 publishers with 5 subscribers 
// over TCP using ZeroMQ's XPUB/XSUB proxy.

// sub (connect) 
//   <-8701-> 
// (bind) xpub <---> xsub (bind) 
//   <-8700-> 
// (connect) pub

var zmq = require('zmq');

// xsub/xpub

var xsub = zmq.socket('xsub');
xsub.bindSync('tcp://*:8700');

var xpub = zmq.socket('xpub');
xpub.setsockopt(zmq.ZMQ_XPUB_VERBOSE, 1);
xpub.bindSync('tcp://*:8701');

// Message pump
xsub.on('message', function (topic, data) {
  xpub.send([ topic, data ]);
});

// Subscription pump
xpub.on('message', function (data) {
  xsub.send(data);
});

// Subscribers
for (var i = 1; i <= 5; i++) {
  (function (i) {
    var subscriber = zmq.socket('sub');
    subscriber.subscribe('Topic 1');
    subscriber.on('message', function (topic, data) {
      console.log('Subscriber', i, 'received', data.toString(), 'on topic', topic.toString());
    });
    subscriber.connect('tcp://localhost:8701');
  })(i);
}

// Publishers
for (var i = 1; i <= 5; i++) {
  (function (i) {
    var publisher = zmq.socket('pub');
    publisher.connect("tcp://localhost:8700");
    var msg = 1;
    setInterval(function () {
      publisher.send(['Topic 1', 'message ' + msg++ + ' from publisher ' + i]);
    }, 500 * i);
  })(i);
}