gistfile1.js

var mmm = require('multi-master-merge');
var leveljs = require('level-js');
var levelup = require('levelup');

var lup = levelup('invoicer', { db: leveljs });
var db = mmm(lup, {encoding: 'json'});

db.put('a', {}, function() {
  db.get('a', function(err, val) {
    console.log(val);
  });
});