code: function createBundleDirectory(location) {
    return fs.mkdir(location)
      .then(onSuccess, onError);
  
    function onSuccess() {
      return location;
    }
  
    function onError(err) {
      if (err.code !== 'EEXIST') {
        throw new Error('! failed to create node_shrinkwrap directory');
      }
      return location;
    }
  }
docs: implementation