How do you use sync in case there are 10 databases.
Do I have to set up 10 new sync?
db = new PouchDB(this.database);
db.sync(remoteCouch, opts1)
db.sync(remoteCouch, opts2)
...
Which means it will open 10 different http connections?
Yes, it does. In that case, you may want to avoid using live replication so you don't keep 10 HTTP connections open. (I.e. just replicate one-at-a-time.)
Or you can replicate from the 10 PouchDBs to a single in-memory PouchDB and then replicate from that to CouchDB (if your databases can fit in memory).