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

var api = this;
  var instanceId;
  var stores = {};
  var revLimit = opts.revs_limit;
  var db;
  var name = opts.name;
  // TODO: this is undocumented and unused probably
  /* istanbul ignore else */
  if (typeof opts.createIfMissing === 'undefined') {
    opts.createIfMissing = true;
  }

  var leveldown = opts.db;

  var dbStore;
  var leveldownName = pouchdbUtils.functionName(leveldown);
  if (dbStores.has(leveldownName)) {
    dbStore = dbStores.get(leveldownName);
  } else {
    dbStore = new pouchdbCollections.Map();
    dbStores.set(leveldownName, dbStore);
  }
  if (dbStore.has(name)) {
    db = dbStore.get(name);
    afterDBCreated();
  } else {
    dbStore.set(name, sublevel(levelup(name, opts, function (err) {
      /* istanbul ignore if */
      if (err) {
        dbStore.delete(name);
        return callback(err);
      }

api._destroy = function (opts, callback) {
    var dbStore;
    var leveldownName = functionName(leveldown);
    /* istanbul ignore else */
    if (dbStores.has(leveldownName)) {
      dbStore = dbStores.get(leveldownName);
    } else {
      return callDestroy(name, callback);
    }

    /* istanbul ignore else */
    if (dbStore.has(name)) {
      levelChanges.removeAllListeners(name);

      dbStore.get(name).close(function () {
        dbStore.delete(name);
        callDestroy(name, callback);
      });
    } else {

api._destroy = function (opts, callback) {
    var dbStore;
    var leveldownName = pouchdbUtils.functionName(leveldown);
    /* istanbul ignore else */
    if (dbStores.has(leveldownName)) {
      dbStore = dbStores.get(leveldownName);
    } else {
      return callDestroy(name, callback);
    }

    /* istanbul ignore else */
    if (dbStore.has(name)) {
      levelChanges.removeAllListeners(name);

      dbStore.get(name).close(function () {
        dbStore.delete(name);
        callDestroy(name, callback);
      });
    } else {

api._destroy = function (opts, callback) {
    var dbStore;
    var leveldownName = functionName(leveldown);
    /* istanbul ignore else */
    if (dbStores.has(leveldownName)) {
      dbStore = dbStores.get(leveldownName);
    } else {
      return callDestroy(name, callback);
    }

    /* istanbul ignore else */
    if (dbStore.has(name)) {
      levelChanges.removeAllListeners(name);

      dbStore.get(name).close(function () {
        dbStore.delete(name);
        callDestroy(name, callback);
      });
    } else {

var api = this;
  var instanceId;
  var stores = {};
  var revLimit = opts.revs_limit;
  var db;
  var name = opts.name;
  // TODO: this is undocumented and unused probably
  /* istanbul ignore else */
  if (typeof opts.createIfMissing === 'undefined') {
    opts.createIfMissing = true;
  }

  var leveldown = opts.db;

  var dbStore;
  var leveldownName = functionName(leveldown);
  if (dbStores.has(leveldownName)) {
    dbStore = dbStores.get(leveldownName);
  } else {
    dbStore = new Map();
    dbStores.set(leveldownName, dbStore);
  }
  if (dbStore.has(name)) {
    db = dbStore.get(name);
    afterDBCreated();
  } else {
    dbStore.set(name, sublevel(levelup(leveldown(name), opts, function (err) {
      /* istanbul ignore if */
      if (err) {
        dbStore.delete(name);
        return callback(err);
      }

api._info = function (callback) {
    var res = {
      doc_count: db._docCount,
      update_seq: db._updateSeq,
      backend_adapter: pouchdbUtils.functionName(leveldown)
    };
    return process.nextTick(function () {
      callback(null, res);
    });
  };

api._info = function (callback) {
    var res = {
      doc_count: db._docCount,
      update_seq: db._updateSeq,
      backend_adapter: pouchdbUtils.functionName(leveldown)
    };
    return process.nextTick(function () {
      callback(null, res);
    });
  };

api._info = function (callback) {
    var res = {
      doc_count: db._docCount,
      update_seq: db._updateSeq,
      backend_adapter: functionName(leveldown)
    }
    return process.nextTick(function () {
      callback(null, res)
    })
  }

api._info = function (callback) {
    var res = {
      doc_count: db._docCount,
      update_seq: db._updateSeq,
      backend_adapter: functionName(leveldown)
    };
    return nextTick(function () {
      callback(null, res);
    });
  };

api._info = function (callback) {
    var res = {
      doc_count: db._docCount,
      update_seq: db._updateSeq,
      backend_adapter: functionName(leveldown)
    };
    return process.nextTick(function () {
      callback(null, res);
    });
  };