MongoDB Error： invalid schema, expected mongodb

我是使用MEAN Stack构建应用程序的新手，我正在try 构建一个实时聊天应用程序，以下是我的服务器端:

console.log("Server running...!");

var mongo=require('mongodb').MongoClient;
var client=require('socket.io').listen(8080).sockets;

mongo.connect('localhost:27017/db/chat',function(err,db){
if(err)  throw err;

client.on('connection',function(socket){
console.log('someone has connected !');

//waiting for input
socket.on('input',function(data){
console.log(data);
});

});

});

我确信我创建了一个名为chat with mongodb的数据库，mongo也在等待连接.但当我用 node 服务器运行服务器时.js发生错误:

Server running...!
C:\Users\azus\Desktop\Psirt\codemaster\node_modules\ mongodb\lib\url_parser.js:20
  throw new Error('invalid schema, expected mongodb');
  ^

Error: invalid schema, expected mongodb
at module.exports (C:\Users\azus\Desktop\Psirt\code-master\node_modules\mong
 odb\lib\url_parser.js:20:11)
at connect (C:\Users\azus\Desktop\Psirt\code-master\node_modules\mongodb\lib
 \mongo_client.js:125:16)
at Function.MongoClient.connect (C:\Users\azus\Desktop\Psirt\code-master\nod
e_modules\mongodb\lib\mongo_client.js:109:3)
at Object.<anonymous> (C:\Users\azus\Desktop\Psirt\code-master\server.js:6:8
)
at Module._compile (module.js:413:34)
at Object.Module._extensions..js (module.js:422:10)
at Module.load (module.js:357:32)
at Function.Module._load (module.js:314:12)
at Function.Module.runMain (module.js:447:10)
at startup (node.js:139:18)

C:\Users\azus\Desktop\Psirt\code-master>

我在这个阶段已经被封锁了好几个星期，有人能帮我吗？

谢谢