title: ZMQ pub/sub subscribe
body: <p>I am having trouble figuring out how to subscribe to a particularly "channel" with ZMQ with regard to its pub/sub functionality.</p>
  
  <p>Here is the publisher:</p>
  
  <pre><code>var zmq = require('zmq');
  var pub = zmq.socket('pub');
  
  pub.bindSync('tcp://127.0.0.1:5555');
  
  setInterval(function(){
      pub.send('pub msg');
  },500);
  </code></pre>
  
  <p>here is the subscriber:</p>
  
  <pre><code> var sub = zmq.socket('sub');
   sub.connect('tcp://127.0.0.1:5555');
  
   sub.subscribe('');  //herein lies the question
  
   sub.on('message',function(msg){
          console.log('Received msg:',msg);
   }
  </code></pre>
  
  <p>This works as is, but the problem is that if I change the argument to sub.subscribe to anything but an empty string (''), the subscriber doesn't receive any messages from the publisher.</p>
  
  <p>How do I configure pub/sub with ZMQ correctly?</p>