title: Difference b/w event.on() and event.once() in nodejs
body: <p>I'm testing the plus_one app, and while running it, I just wanted to clarify my concepts on event.once() and event.on()</p>
  
  <p>This is plus_one.js</p>
  
  <pre><code>&gt; process.stdin.resume();
  process.stdin.on('data',function(data){
      var number;
      try{
          number=parseInt(data.toString(),10);
          number+=1;
          process.stdout.write(number+"\n");
          }
      catch(err){
          process.stderr.write(err.message+"\n");
          }
      });
  </code></pre>
  
  <p>and this is test_plus_one.js</p>
  
  <pre><code>var spawn=require('child_process').spawn;
  var child=spawn('node',['plus_one.js']);
  
  setInterval(function(){
      var number=Math.floor(Math.random()*10000);
      child.stdin.write(number+"\n");
      child.stdout.on('data',function(data){
          console.log('child replied to '+number+' with '+data);
          });
      },1000);
  </code></pre>
  
  <p>I get few maxlistener offset warning while using child.stdin.on() but this is not the case when using child.stdin.once(), why is this happening ?</p>
  
  <p>Is it because child.stdin is listening to previous inputs ? but in that case maxlistener offset should be set more frequently, but its only happening for once or twice in a minute.</p>