code: function Storage(mongoURI, mongoOptions, storageOptions) {
    if (!(this instanceof Storage)) {
      return new Storage(mongoURI, mongoOptions, storageOptions);
    }
  
    assert(typeof mongoOptions === 'object', 'Invalid mongo options supplied');
  
    this._uri = mongoURI;
    this._options = mongoOptions;
  
    const defaultLogger = {
      info: console.log,
      debug: console.log,
      error: console.error,
      warn: console.warn
    };
    this._log = defaultLogger;
    if (storageOptions && storageOptions.logger) {
      this._log = storageOptions.logger;
    }
  
    // connect to the database
    this._connect();
  }
docs: MongoDB storage interface
  @constructor
  @param {Object} mongoConf
  @param {Object} options