PouchDB to CouchDB sync saves filters as views

I have simple PouchDB instances one for local browser and one remote. I have a design doc that takes a filter, when I issue a sync it saves as a view.

var localDB = new PouchDB('mydb');
var remoteDB = new PouchDB('http://anna:secret@127.0.0.1:5984/db');

When I execute the below it saves as a view

localDB.sync(remoteDB)

{
    "_id": "_design/sync",
    "_rev": "2-f6db221d90157a99f4e6e9e6e27ffe85",
    "views": {
        "by_user": {
            "map": "function (doc) {\n  emit(doc._id, 1);\n}"
        }
    }
}

when it is written as below on my client script

localDB.put({
        _id : '_design/sync',
        filters: {
            by_user : function(doc, req) {
                return doc._id.indexOf(req.query.user) > 0;
            }.toString()
        }
    }).then().catch(function(err) {});

So, why can't I see filters in my document when viewed in CouchDB ?