title: Customizing fs module it returns undefined
body: <p>So I'm trying to make fs module object oriented and i made this method it returns <code>undefined</code> but when i remove it and run it it works. whats wrong?</p>
  <pre class="lang-js prettyprint-override"><code>readFileAsync = () =&gt; {
          fs.readFile(this.filename, (err, data) =&gt; {
              if (err) {
                  throw new err;
              } else {
                  return data.toString();
              }
          })
  }
  </code></pre>