title: Meaning or source code for callback() in node.js chat app
body: <p>I'm trying to go through the source code for the node chat demo <a href="https://github.com/ry/node_chat" rel="nofollow">seen here</a>.  In the server.js file and fu.js file there is a function referenced as callback() seen here:</p>
  
  <pre><code>function loadResponseData(callback) { 
  if (body &amp;&amp; headers &amp;&amp; !DEBUG) { //if they already have value
    callback();
    return;
  }...
  </code></pre>
  
  <p>but as far as I can tell this function is never defined and I cannot find it as a module function of node.js, a function of jquery or a standard function for javascript.</p>
  
  <p>I think I understand how callback functions work but I'm not familiar with this call and it is used frequently enough in this app that I would like a firm understanding of what it is and where it comes from.</p>
  
  <p>So my question is three fold:
  1) where is the function based: (javascirpt, jquery, node.js, particular to this app)
  2) where can I find the source code for this function?
  3) how is this function interacting with the functions it is called in?</p>