Can't connect to a MongoDB using Node.js
Solution 1:
First make sure your MongoDB server is running by running mongod in the directory that MongoDB is installed.
Then see what port it is running on ( usually it's 27017 ) . Then update your URL in your code and you're good to go .
Solution 2:
Your error explaining itself.
Mongo cant find default db path B:/data/db.
Create this folder or on start up choose another DB directory
mongod --dbpath yourPath(C:\myDb)
Also default mongo port is 27017 so you need to change connection string like this "mongodb://@localhost:27017/dbYouWant"
Hope this helps.