code: function _logProgress(req) {
    req.on('response', function(resp) {
      var len = parseInt(resp.headers['content-length'], 10),
        bar = new ProgressBar('[:bar]', {
          complete: '=',
          incomplete: ' ',
          total: len,
          width: 100, // just use 100
        });
  
      req.on('data', function(chunk) {
        bar.tick(chunk.length);
      });
    });
  
    req.on('error', function(err) {
      console.log(err);
      _log('error', 'failed to download node sources,');
      process.exit(1);
    });
  
    return req;
  }
docs: Log the progress of a request object.