mongos.connect("mongodb://localhost/Company")
On executing the above command as per the document if Company database exits then it will be connected to the nodejs or else database will be created and then connection is made.
My question is where will this newly created database exist in mongodb data folder or nodejs application folder
So your application is connecting to localhost where you have MongoDB server running on the default port (27017). If you are connected to a MongoDB cluster using a mongos process you will have to see where the mongod (database process itself) is/are running. Let's take the simple case where your mongod is running locally.
So I expect you have started your MongoDB instance with all default values, the "database files" are created in /data/db ( \data\db ).
This means that in your case, you should see the "Company" db files in this folder, something like :
/data/db/Company.0
/data/db/Company.ns
Let's now give you more informations about this:
When you start your database you start a "mongod", that use a parameter named dbpath (see http://docs.mongodb.org/manual/reference/configuration-options/#storage.dbPath ) that is defaulted to /data/db
You can override it to any existing folder to adapt to your environment.
So nothing is "created" inside your application, everything in done at the"mongodb" (database) level.