Using Pouchdb _selector plug-in

my_code.js

import PouchDB from 'pouchdb-browser'  // Or however you are importing PouchDB using your module system

PouchDB.plugin((PouchDB) => { // Add the 'plug-in' to the Pouchdb instance
  let pouchReplicate = PouchDB.replicate

  PouchDB.replicate = (source, target, repOptions) => {

    let sourceAjax = source._ajax
    source._ajax = (ajaxOps, callback) => {
      if (ajaxOps.url.includes('_selector')) {
        ajaxOps.url = ajaxOps.url.replace('filter=_selector%2F_selector', 'filter=_selector')
        ajaxOps.method = 'POST'
        ajaxOps.body = {
          selector: repOptions.selector
        }
      }
      return sourceAjax(ajaxOps, callback)
    }
    return pouchReplicate(source, target, repOptions)
  }
})

let remotedb = new PouchDB('http://my.couchd.db:5984/database')

// put some docs in the remote db
remotedb.bulkDocs([
  {kind: 'apple'},
  {kind: 'orange'},
  {kind: 'pear'}
])

let localdb = new PouchDB('mydb')

PouchDB.replicate(remotedb, localdb, {
  filter: '_selector',
  selector: {
    kind: {
      $in: [
        'apple',
        'pear',
      ]
    }
  }
})

// Now localdb only has 'apple' and 'pear' documents