Connect MongoDB with Node app using MongooseJS
                     Connect MongoDB with Node app 
using MongooseJS
      Connect the MongoDB database by using MongooseJS to the NodeJS application. 
Before we dive into watching how the MongoDB connects with a Nodejs app using 
mongooseJS, let's get a quick intro to these technologies which are ruling the online 
development domain of today.
• Node: Node.js (Node) is an open-source development platform that is used for 
executing JavaScript code server-side. Node is beneficial for developing applications 
that need a persistent connection from the browser to the server and is usually used 
for real-time applications like chat, news feeds, and web push notifications.
• MongoDB: MongoDB may be a cross-platform and open-source document-oriented 
database, a sort of NoSQL database. As a NoSQL(not only SQL) database, MongoDB 
reject the relational database’s table-based structure to adapt JSON-like documents 
that have dynamic schemas which it calls BSON(Binary JSON).
      
• MongooseJS: Mongoose or MongooseJS may be a MongoDB object 
modeling(ODM) tool designed to figure in an asynchronous environment. 
Basically, it's a package that we'll use to interact(query, update, 
manipulate) with our MongoDB database in our nodeJS app. we might 
install or ‘require’ mongooseJS in our app with NPM(node packaging 
manager)
• NPM: Node Package Manager or NPM is that the official package 
manager for nodeJS applications. it'll come installed with NodeJS. it's used 
from the instruction or terminal(depending on what OS is being used).
    So now that we are well-known with the basic definitions of these 
technologies, let's dive into the code and its explanations. Our NodeJS app 
during this case(for demo purpose) goes to be one JavaScript file. Let’s call 
it app.js. move ahead and create that file in a new folder.

Source code explanation:
   Line2: It needs or imports the mongoose package in our app.
   Line4: It assigns the connection string which contains the data about the connection to our MongoDB 
variable.
   Line6: These lines help in establishing or ‘open’ or stir up a reference to the database mentioned within 
the MongoDB variable. the primary argument to the mongoose.connect() function is that the 
connection string(the MongoDB variable).
    
 Line10: The mongoose.connect() function returns the connection to the database 
as mongoose.connection which we assign to the DB variable.
  Line14: This line logs the message into the console when the connection to the 
database has been created and came back. It listens for ‘connected’ event and 
once the event fires, the function() comprising of line 14,15,16 gets executed.
  Line19: This line logs the message into the console when the connection to the 
database has been created and came back. It listens for the ‘error’ event and once 
the event fires, the function() comprising of line 19,20,21 gets executed.
    After writing the source code open a terminal or the command prompt(in case of 
windows users) and navigate to your project directory. Then write the command 
npm install mongoose as shown within the image below:
 

   The above command will create a ‘node_modules’ folder in your current 
directory or folder and download the required files there.
   If you're following so far , all the preparation is completed and now we will 
test our connection to database.
      Write node app.js to start out the app.

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