How to use the pouchdb-core.default function in pouchdb-core

let PouchDB;
if(typeof process !== 'undefined' && process.versions && process.versions.node) {
  PouchDB = require('pouchdb-core')
    .plugin(require('pouchdb-adapter-http'))
    .plugin(require('pouchdb-replication'))
    .plugin(require('pouchdb-mapreduce'))
    .plugin(require('pouchdb-find'))
    .plugin(require('pouchdb-adapter-memory'));
}
else {
  if(window.PouchDB) {
    PouchDB = window.PouchDB;
  }
  else {
    PouchDB = window.PouchDB = require('pouchdb-core').default
      .plugin(require('pouchdb-adapter-http').default)
      .plugin(require('pouchdb-replication').default)
      .plugin(require('pouchdb-mapreduce').default)
      .plugin(require('pouchdb-find').default)
      .plugin(require('pouchdb-adapter-idb').default);
  }
}
var PouchDB$1 = PouchDB;

function adapter({AbstracrAdapter}) {
  const fieldsToDelete = '_id,search,timestamp'.split(',');
  return class AdapterPouch extends AbstracrAdapter {
    constructor($p) {
      super($p);
      this.props = {
        _data_loaded: false,

'use strict'

var bluebird = require('bluebird')
var path = require('path')
var adapterHttp = require('pouchdb-adapter-http')
var adapterFind = require('pouchdb-find')
var adapterReplication = require('pouchdb-replication')
var PouchDbCore = require('pouchdb-core')
var PouchDB = PouchDbCore.default || PouchDbCore
PouchDB.plugin(adapterHttp.default || adapterHttp)
  .plugin(adapterFind.default || adapterFind)
  .plugin(adapterReplication.default || adapterReplication)
PouchDB.utils = { promise: bluebird }
var privateMethods = require('./private')
var publicMethods = require('./public')

var assign = require('lodash/assign')
var isNil = require('lodash/isNil')
var toArray = require('lodash/toArray')

/**
 * @namespace
 * @property Pouchy.PouchDB
 * tap into the PouchDB constructor via Pouchy
 */

*/
if(typeof process !== 'undefined' && process.versions && process.versions.node) {
  PouchDB = require('pouchdb-core')
    .plugin(require('pouchdb-adapter-http'))
    .plugin(require('pouchdb-replication'))
    .plugin(require('pouchdb-mapreduce'))
    .plugin(require('pouchdb-find'))
    .plugin(require('pouchdb-adapter-memory'));
}
else {
  if(window.PouchDB) {
    PouchDB = window.PouchDB;
  }
  else {
    //const ua = (typeof navigator !== 'undefined' && navigator.userAgent) ? navigator.userAgent.toLowerCase() : '';
    PouchDB = window.PouchDB = require('pouchdb-core').default
      .plugin(require('pouchdb-adapter-http').default)
      .plugin(require('pouchdb-replication').default)
      .plugin(require('pouchdb-mapreduce').default)
      .plugin(require('pouchdb-find').default)
      .plugin(require('pouchdb-adapter-idb').default);
  }
}

export default PouchDB;