Using older versions of node and npm when install mongodb you have different versions:

npm install mongodb- node 0.10.38 - 2.1.22-alpha4
npm install mongodb- node 4.4.5 - 2.1.21

On mongodb alpha versions we have a bug when a replica set member is down(in this example the SEC).

var CONNECTION_URL = 'mongodb://' + [MASTER, SECONDARY].join(',') + '/' + DB;

If the connection url have the master and the secondary the process will crash with this error:

d:\test\node_modules\mongodb\lib\server.js:231
process.nextTick(function()

Unknown macro: { throw err; }

)
^
TypeError: Cannot read property 'hosts' of null
at connectFunction (d:\test\node_modules\mongodb\lib\mongo_client.js:327:23)
at open (d:\test\node_modules\mongodb\lib\db.js:242:14)
at Server.connect.connectErrorHandler (d:\test\node_modules\mongodb\lib\server.js:229:9)
at g (events.js:180:16)
at emit (events.js:98:17)
at reconnectErrorHandler (d:\test\node_modules\mongodb\node_modules\mongodb-core\lib\topologies\server.js:138:12)
at g (events.js:180:16)
at emit (events.js:98:17)
at errorHandler (d:\test\node_modules\mongodb\node_modules\mongodb-core\lib\connection\pool.js:126:12)
at g (events.js:180:16)

If the connection url have only reacheable members, everything is ok.

var CONNECTION_URL = 'mongodb://' + MASTER + '/' + DB;

I've attached the code.

The question is why on older npm's is installed mongodb alpha?