How to use the pouchdb-merge.winningRev function in pouchdb-merge

function insertDoc(docInfo, resultsIdx, callback) {
    // Cant insert new deleted documents
    var winningRev = calculateWinningRev(docInfo.metadata);
    var deleted = isDeleted(docInfo.metadata, winningRev);
    if ('was_delete' in opts && deleted) {
      results[resultsIdx] = createError(MISSING_DOC, 'deleted');
      return callback();
    }

    // 4712 - detect whether a new document was inserted with a _rev
    var inConflict = newEdits && rootIsMissing(docInfo);

    if (inConflict) {
      var err = createError(REV_CONFLICT);
      results[resultsIdx] = err;
      return callback();
    }

    var delta = deleted ? 0 : 1;

cursor.onsuccess = function (e) {
      var cursor = e.target.result;
      if (!cursor) {
        return; // done
      }
      var metadata = decodeMetadataCompat(cursor.value);

      metadata.winningRev = metadata.winningRev ||
        calculateWinningRev(metadata);

      function fetchMetadataSeq() {
        // metadata.seq was added post-3.2.0, so if it's missing,
        // we need to fetch it manually
        var start = metadata.id + '::';
        var end = metadata.id + '::\uffff';
        var req = bySeqStore.index('_doc_id_rev').openCursor(
          IDBKeyRange.bound(start, end));

        var metadataSeq = 0;
        req.onsuccess = function (e) {
          var cursor = e.target.result;
          if (!cursor) {
            metadata.seq = metadataSeq;
            return onGetMetadataSeq();
          }

function getWinningRev(metadata) {
  return 'winningRev' in metadata ?
    metadata.winningRev : pouchdbMerge.winningRev(metadata);
}

function getWinningRev(metadata) {
  return 'winningRev' in metadata ?
    metadata.winningRev : calculateWinningRev(metadata);
}

function getWinningRev(metadata) {
  return 'winningRev' in metadata ?
    metadata.winningRev : pouchdbMerge.winningRev(metadata);
}

function getWinningRev(metadata) {
  return 'winningRev' in metadata ?
    metadata.winningRev : calculateWinningRev(metadata);
}