title: fs library : Error when use it
body: <p>I use <code>fs</code> library for reading file from system. I don't know I use this library and meet error. </p>
  
  <ol>
  <li><p>I'm using PhpStorm. at line : <code>fs.readFile()</code> : there's a line under that, that notice me : unresolved function or method readFile(). It means IDE doesn't figure out where is this function. Nevertheless, I have checked <code>fs.js</code> and I see no problem.</p></li>
  <li><p>I receive this error when running:</p></li>
  </ol>
  
  <blockquote>
    <p>events.js:72
            throw er; // Unhandled 'error' event
                  ^ Error: listen EADDRINUSE
        at errnoException (net.js:901:11)
        at Server._listen2 (net.js:1039:14)
        at listen (net.js:1061:10)
        at Server.listen (net.js:1127:5)
        at Object. (/home/hqt/PhpstormProjects/NodeApp/sample/AsynchronouslyReading.js:21:4)
        at Module._compile (module.js:456:26)
        at Object.Module._extensions..js (module.js:474:10)
        at Module.load (module.js:356:32)
        at Function.Module._load (module.js:312:12)
        at Function.Module.runMain (module.js:497:10)</p>
  </blockquote>
  
  <p>Here is my code :</p>
  
  <pre><code>var http = require('http');
  var fs = require('fs');
  
  // create http server
  http.createServer(function(req, res) {
      fs.readFile('helloworld.js', 'utf-8', function(err, data) {
          res.writeHead(200, {'content-type' : 'text/plain'});
          if (err) res.write('could not find or open file');
          else res.write(data);
  
          // ending
          res.end();
      });
  }).listen(8124, function() {console.log('server is running at 8124');});
  
  console.log('server is runnint at 8124 port');
  </code></pre>
  
  <p>Please help me figure out why. I'm using Ubuntu machine for development.</p>
  
  <p>Thanks :)</p>