Since mongodb-core 3.2.0, connection failure on first connect no longer throws a MongoNetworkError. Instead, an unwrapped error from TCPConnectWrap is thrown.

How to recreate:

1. Create a new Node.js project. Then, install mongodb-core 3.2.0.
2. Add this code to index.js:

    var Server = require('mongodb-core').Server
    var server = new Server({
      host: 'localhost'
      , port: 27017
      , reconnect: true
      , reconnectInterval: 50
    });
    server.connect();
   

   (This code is actually straight from the documentation.)

3.  Make sure no server is listening on that port, then run node index.js
   Expected result: Node stops with MongoNetworkError, as it was on mongodb-core 3.1
   Actual result: Node stops with the following error:

     events.js:183
        throw er; // Unhandled 'error' event
        ^
   
   Error: connect ECONNREFUSED 127.0.0.1:27017
        at TCPConnectWrap.afterConnect [as oncomplete] (net.js:1191:14)
   

For reference, this is how the error looks like on mongodb-core 3.1.11 (the lastest version on 3.1 line):

events.js:183
      throw er; // Unhandled 'error' event
      ^
 
MongoNetworkError: failed to connect to server [localhost:27017] on first connect [MongoNetworkError: connect ECONNREFUSED 127.0.0.1:27017]
    at Pool.<anonymous> (<project dir>/node_modules/mongodb-core/lib/topologies/server.js:564:11)
    at emitOne (events.js:116:13)
    at Pool.emit (events.js:211:7)
    at Connection.<anonymous> (<project dir>/node_modules/mongodb-core/lib/connection/pool.js:317:12)
    at Object.onceWrapper (events.js:317:30)
    at emitTwo (events.js:126:13)
    at Connection.emit (events.js:214:7)
    at Socket.<anonymous> (<project dir>/node_modules/mongodb-core/lib/connection/connection.js:246:50)
    at Object.onceWrapper (events.js:315:30)
    at emitOne (events.js:116:13)