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

// store the value of update_seq in the by-sequence store the key name will
// never conflict, since the keys in the by-sequence store are integers
var UPDATE_SEQ_KEY = '_local_last_update_seq';
var DOC_COUNT_KEY = '_local_doc_count';
var UUID_KEY = '_local_uuid';

var MD5_PREFIX = 'md5-';

var safeJsonEncoding = {
  encode: pouchdbJson.safeJsonStringify,
  decode: pouchdbJson.safeJsonParse,
  buffer: false,
  type: 'cheap-json'
};

var levelChanges = new pouchdbUtils.changesHandler();

// winningRev and deleted are performance-killers, but
// in newer versions of PouchDB, they are cached on the metadata
function getWinningRev(metadata) {
  return 'winningRev' in metadata ?
    metadata.winningRev : pouchdbMerge.winningRev(metadata);
}

function getIsDeleted(metadata, winningRev) {
  return 'deleted' in metadata ?
    metadata.deleted : pouchdbAdapterUtils.isDeleted(metadata, winningRev);
}

function fetchAttachment(att, stores, opts) {
  var type = att.content_type;
  return new Promise(function (resolve, reject) {

// API implementations
import info from './info';
import get from './get';
import getAttachment from './getAttachment';
import bulkDocs from './bulkDocs';
import allDocs from './allDocs';
import changes from './changes';
import getRevisionTree from './getRevisionTree';
import doCompaction from './doCompaction';
import destroy from './destroy';

var ADAPTER_NAME = 'indexeddb';

// TODO: Constructor should be capitalised
var idbChanges = new changesHandler();

// A shared list of database handles
var openDatabases = {};

function IdbPouch(dbOpts, callback) {

  var api = this;
  var metadata = {};

  // This is a wrapper function for any methods that need an
  // active database handle it will recall itself but with
  // the database handle as the first argument
  var $ = function (fun) {
    return function () {
      var args = Array.prototype.slice.call(arguments);
      setup(openDatabases, api, dbOpts).then(function (res) {

import get from './get';
import { getAttachment } from './getAttachment';
import bulkDocs from './bulkDocs';
import allDocs from './allDocs';
import changes from './changes';
import getRevisionTree from './getRevisionTree';
import doCompaction from './doCompaction';
import destroy from './destroy';
import {query, viewCleanup} from './find';

import { DOC_STORE } from './util';

var ADAPTER_NAME = 'indexeddb';

// TODO: Constructor should be capitalised
var idbChanges = new changesHandler();

// A shared list of database handles
var openDatabases = {};

function IdbPouch(dbOpts, callback) {

  var api = this;
  var metadata = {};

  // Wrapper that gives you an active DB handle. You probably want $t.
  var $ = function (fun) {
    return function () {
      var args = Array.prototype.slice.call(arguments);
      setup(openDatabases, api, dbOpts).then(function (res) {
        metadata = res.metadata;
        args.unshift(res.idb);

// store the value of update_seq in the by-sequence store the key name will
// never conflict, since the keys in the by-sequence store are integers
var UPDATE_SEQ_KEY = '_local_last_update_seq';
var DOC_COUNT_KEY = '_local_doc_count';
var UUID_KEY = '_local_uuid';

var MD5_PREFIX = 'md5-';

var safeJsonEncoding = {
  encode: safeJsonStringify,
  decode: safeJsonParse,
  buffer: false,
  type: 'cheap-json'
};

var levelChanges = new Changes();

// winningRev and deleted are performance-killers, but
// in newer versions of PouchDB, they are cached on the metadata
function getWinningRev(metadata) {
  return 'winningRev' in metadata ?
    metadata.winningRev : calculateWinningRev(metadata);
}

function getIsDeleted(metadata, winningRev) {
  return 'deleted' in metadata ?
    metadata.deleted : isDeleted(metadata, winningRev);
}

function fetchAttachment(att, stores, opts) {
  var type = att.content_type;
  return new Promise(function (resolve, reject) {

// store the value of update_seq in the by-sequence store the key name will
// never conflict, since the keys in the by-sequence store are integers
var UPDATE_SEQ_KEY = '_local_last_update_seq';
var DOC_COUNT_KEY = '_local_doc_count';
var UUID_KEY = '_local_uuid';

var MD5_PREFIX = 'md5-';

var safeJsonEncoding = {
  encode: pouchdbJson.safeJsonStringify,
  decode: pouchdbJson.safeJsonParse,
  buffer: false,
  type: 'cheap-json'
};

var levelChanges = new pouchdbUtils.changesHandler();

// winningRev and deleted are performance-killers, but
// in newer versions of PouchDB, they are cached on the metadata
function getWinningRev(metadata) {
  return 'winningRev' in metadata ?
    metadata.winningRev : pouchdbMerge.winningRev(metadata);
}

function getIsDeleted(metadata, winningRev) {
  return 'deleted' in metadata ?
    metadata.deleted : pouchdbAdapterUtils.isDeleted(metadata, winningRev);
}

function fetchAttachment(att, stores, opts) {
  var type = att.content_type;
  return new Promise(function (resolve, reject) {

// store the value of update_seq in the by-sequence store the key name will
// never conflict, since the keys in the by-sequence store are integers
var UPDATE_SEQ_KEY = '_local_last_update_seq';
var DOC_COUNT_KEY = '_local_doc_count';
var UUID_KEY = '_local_uuid';

var MD5_PREFIX = 'md5-';

var safeJsonEncoding = {
  encode: safeJsonStringify,
  decode: safeJsonParse,
  buffer: false,
  type: 'cheap-json'
};

var levelChanges = new Changes();

// winningRev and deleted are performance-killers, but
// in newer versions of PouchDB, they are cached on the metadata
function getWinningRev(metadata) {
  return 'winningRev' in metadata ?
    metadata.winningRev : calculateWinningRev(metadata);
}

function getIsDeleted(metadata, winningRev) {
  return 'deleted' in metadata ?
    metadata.deleted : isDeleted(metadata, winningRev);
}

function fetchAttachment(att, stores, opts) {
  var type = att.content_type;
  return new Promise(function (resolve, reject) {

// store the value of update_seq in the by-sequence store the key name will
// never conflict, since the keys in the by-sequence store are integers
var UPDATE_SEQ_KEY = '_local_last_update_seq'
var DOC_COUNT_KEY = '_local_doc_count'
var UUID_KEY = '_local_uuid'

var MD5_PREFIX = 'md5-'

var safeJsonEncoding = {
  encode: safeJsonStringify,
  decode: safeJsonParse,
  buffer: false,
  type: 'cheap-json'
}

var levelChanges = new Changes()

// winningRev and deleted are performance-killers, but
// in newer versions of PouchDB, they are cached on the metadata
function getWinningRev (metadata) {
  return 'winningRev' in metadata
    ? metadata.winningRev
    : calculateWinningRev(metadata)
}

function getIsDeleted (metadata, winningRev) {
  return 'deleted' in metadata
    ? metadata.deleted
    : isDeleted(metadata, winningRev)
}

function fetchAttachment (att, stores, opts) {

} from './constants';

import {
  qMarks,
  stringifyDoc,
  unstringifyDoc,
  select,
  compactRevs,
  websqlError,
  getSize,
  unescapeBlob
} from './utils';

import openDB from './openDatabase';

var websqlChanges = new Changes();

function fetchAttachmentsIfNecessary(doc, opts, api, txn, cb) {
  var attachments = Object.keys(doc._attachments || {});
  if (!attachments.length) {
    return cb && cb();
  }
  var numDone = 0;

  function checkDone() {
    if (++numDone === attachments.length && cb) {
      cb();
    }
  }

  function fetchAttachment(doc, att) {
    var attObj = doc._attachments[att];

const resolveResult = meta => {
      const result = {
        storage,
        meta: {
          db_uuid: meta[0],
          doc_count: meta[1],
          update_seq: meta[2]
        },
        opts,
        changes: new ChangesHandler()
      }

      openDatabases[opts.name] = result
      resolve(result)
    }