Can't connect to MongoDB database with NodeJS native driver

Question

I have a NodeJS app in which I need to connect to to MongoDB databases - one a single server set up, and the second from a replica set. I connect to the next one just fine, but when connecting to the second one - I get the following error:

/Users/iddogino/Documents/RapidApp/node_modules/mongodb/lib/mongodb/db.js:299
          throw err;
                ^
TypeError: Cannot set property 'auto_reconnect' of undefined
    at /Users/iddogino/Documents/RapidApp/node_modules/mongodb/lib/mongodb/connection/repl_set/options.js:110:35
    at Array.forEach (native)
    at Options.decorateAndClean (/Users/iddogino/Documents/RapidApp/node_modules/mongodb/lib/mongodb/connection/repl_set/options.js:108:16)
    at new exports.ReplSet (/Users/iddogino/Documents/RapidApp/node_modules/mongodb/lib/mongodb/connection/repl_set/repl_set.js:84:31)
    at /Users/iddogino/Documents/RapidApp/node_modules/mongodb/lib/mongodb/mongo_client.js:320:30
    at /Users/iddogino/Documents/RapidApp/node_modules/mongodb/lib/mongodb/db.js:296:11
    at process._tickDomainCallback (node.js:459:13)

The code I use to connect (after omitting user names and real urls) is:

require('mongodb').MongoClient.connect("mongodb://password@url1:port1,url2:port2/dbName?replicaSet=setName&w=0&readPreference=secondary", function(err, doc) {...});

Now when I tried this alone (not after the code connecting to true other DB), I worked just fine... Any ideas?

Answer 1

This one took me a minute to figure out. The error says the problem is in ./node_modules/mongodb/lib/mongodb/connection/repl_set/options.js:110

The issue is that options.js:91 creates an empty object. They're doing this make a dictionary and deduplicate the 'host:port' strings for the servers. options.js:104 loops through the keys in that dictionary and blindly loads them into an array. This would be a problem if you have added something to Object.prototype globally since it would also get added to the final array of servers. Since whatever you've added to Object.prototype probably isn't a server, it won't have an options property and you'll get this error.

Work around: Figure out where in your code you have modified Object.prototype and make it less general. I think they've updated this in newer versions of the driver, but if you're using an old one you need to work around it.