title: In fs.writeFile([option]), how an "options parameter" generally work?
body: <p>I was reading this document about Node.js file system, <a href="http://nodejs.org/api/fs.html#fs_fs_writefile_filename_data_options_callback" rel="noreferrer"><code>fs.writeFile(filename, data, [options], callback)</code></a>.
  So I noticed that i have seen the [options] pretty often, but never used it for anything. Can someone give me an example? All the cases i had didn't use this option.</p>