ascript.js

var start = document.getElementById('start');
var stuff = document.getElementById('stuff');
var remote = new PouchDB('http://registry.npmjs.org/', {cache: true});
var local = new PouchDB('npm');
start.addEventListener('click', function (){
  remote.info().then(function (a) {
    return a.doc_count;
  }).then(function (count) {
     remote.replicate.to(local, {
       batch_size: 100
     }).on('change', function (change) {
       stuff.innerText = change.docs_written + ' out of ' + count;
     }).on('complete', function () {
       stuff.innerText = change.docs_written + ' done'
     });
  });
});

index.html

<div id="stuff"></div>
<button id="start">start</button>
<script src="//pouchtest.com/couchdb/pouchdb_builds/e8a764e9a58da8e8f26a069df5d75cc6f2acd8a7/pouchdb.min.js"></script>
<script src="ascript.js"></script>