Google storage platform: list only prefixes (directories) of given prefix(directory)

gcp-prefixes.js

  const Storage = require('@google-cloud/storage');

  function getPrefixes(cred, bucketName, queryParams = {}) {
    return new Promise((resolve, reject) => {
      new Storage(cred)
        .bucket(bucketName)
        .request({
          uri: '/o',
          qs: {
            delimiter: queryParams.delimiter || '/',
            prefix: queryParams.prefix || ''
          }
        }, (err, response) => {
          err ? reject(err) : resolve(response.prefixes || []);
        });    
    });
  }