code: function _timestampBeforeNow(timestamp) {
        if(!(typeof timestamp === 'string' && dateRegEx.test(timestamp))) {
          throw new TypeError('`revoked` timestamp must be a string.');
        }
        const now = new Date();
        const tsDate = new Date(timestamp);
        return tsDate < now;
      }
docs: returns true if the given timestamp is before the current time