How to use the pouchdb-utils.pick function in pouchdb-utils

function cleanDocs(docs) {
  for (var i = 0; i < docs.length; i++) {
    var doc = docs[i];
    if (doc._deleted) {
      delete doc._attachments; // ignore atts for deleted docs
    } else if (doc._attachments) {
      // filter out extraneous keys from _attachments
      var atts = Object.keys(doc._attachments);
      for (var j = 0; j < atts.length; j++) {
        var att = atts[j];
        doc._attachments[att] = pick(doc._attachments[att],
          ['data', 'digest', 'content_type', 'length', 'revpos', 'stub']);
      }
    }
  }
}

function cleanDocs(docs) {
  for (var i = 0; i < docs.length; i++) {
    var doc = docs[i];
    if (doc._deleted) {
      delete doc._attachments; // ignore atts for deleted docs
    } else if (doc._attachments) {
      // filter out extraneous keys from _attachments
      var atts = Object.keys(doc._attachments);
      for (var j = 0; j < atts.length; j++) {
        var att = atts[j];
        doc._attachments[att] = pick(doc._attachments[att],
          ['data', 'digest', 'content_type', 'length', 'revpos', 'stub']);
      }
    }
  }
}

var numBatches = Math.ceil(opts.docs.length / batchSize);
      var numDone = 0;
      var results = new Array(numBatches);

      function onResult(batchNum) {
        return function (err, res) {
          // err is impossible because shim returns a list of errs in that case
          results[batchNum] = res.results;
          if (++numDone === numBatches) {
            callback(null, {results: flatten(results)});
          }
        };
      }

      for (var i = 0; i < numBatches; i++) {
        var subOpts = pick(opts, ['revs', 'attachments', 'binary', 'latest']);
        subOpts.docs = opts.docs.slice(i * batchSize,
          Math.min(opts.docs.length, (i + 1) * batchSize));
        bulkGetShim(self, subOpts, onResult(i));
      }
    }

api._getAttachment(doc._id, att, attObj, attOpts, function (_, data) {
      doc._attachments[att] = Object.assign(
        pick(attObj, ['digest', 'content_type']),
        { data: data }
      );
      checkDone();
    });
  }

readBlobData(body, type, asBlob, function (data) {
            row.doc._attachments[att] = Object.assign(
              pick(attObj, ['digest', 'content_type']),
              {data: data}
            );
            resolve();
          });
        });