calculate sha1 for a file with nodejs

var file = fs.createReadStream(path);
  var sha1_for_file = crypto.createHash('sha1');

  file.addListener('error', function(err) {
    throw err;
  });
  file.addListener('data', function(data) {
    sha1_for_file.update(data);
  });
  file.addListener('close', function() {
    return sha1_for_file.digest('hex');
  });