// we will use sys.log for logging
var sys = require('sys');
// send open file command, with callback
fs.open('path/to/file.js', 'w', 0777, function(err, fd) {
  //throw error, if there was one
  if (err) throw err;
  // send write command with opened file, content, starting point, encoding and callback
  fs.write(fd, 'Hello World!', 0, 'utf8', function (err, written) {
    //throw error, if there was one
    if (err) throw err;
    // after successful file write, log number of bytes written
    sys.log('Success! Wrote ' + written + ' bytes');
  });
});