func.js

function listMongoCollections(db) {
  return db .listCollections()
            .toArray()
            .map(doc => {
              return db.collection(doc.name).count().then(count => {
                doc.count = count
                return doc;
              })
            })
            .all();
}

const {props} = Promise;
const {assign} = Object;
const count =  (db, doc) => db.collection(doc.name).count();
const listMongoCollections = db => db.listCollections().toArray().map(doc => props(assign(doc, {count: count(db, doc)));