Node.js How to truncate response for HEAD requests?

I am writing a Node.js HTTP server. For HEAD requests I would use the GET code path especially for calculating the content size etc. How to skip sending the body afterwards? I imagine the following example

var http = require('http');
http.createServer(function (req, res) {
  res.writeHead(200, {'Content-Type': 'text/plain'});
  res.write('Hello World\n');

  if(req.method === 'HEAD') {
    res.dropBody(); // omit the body
  }    
  res.end(); // just send the headers
}).listen(1337, '127.0.0.1');
console.log('Server running at http://127.0.0.1:1337/');