Refactoring to continuation-passing

index.js

var http = require('http');
var bl = require('bl');

function start(callback) {
  option = {};
  options.path = '/start';
  var req = http.request(options, function (res) { res.pipe(bl(callback)) });
  req.end();
}

start(function (err, startingRoomId) {
  if (err) {
    console.warn(err);
  } else {
    console.log(startingRoomId.toString());
  }
});