Go inside the folder cd backend
npm init
create entry point server.js
npm install nodemon express dotenv cors  

inside pakage.json 
script: {C:\Users\Parveen\Desktop\reactnode\reactfrontend\nodebackend\routes\route.js
"start": nodemon server.js
}
In server .js 

const express = require('express')
const app = express()
app.listen(4000,()=> console.log("server is up and running"))
 
 on console - nodemon server.js
 
Create a Folder routes
inside it  create a file - router.js
const express = require("express")
const router = express.Router()

ok before going ahead create schema inside model folder
call it - modelform.js
const mongoose = require('mongoose')

const signUpTemplate= new mongoose.Schema({
    fullName:{
        type:String,
    
    },
    username:{
        type:String,
       
    },
    email:{
        type:String,
  
    },
    password:{
        type:String,
     
        },
     date:{
         type:Date,
        default:Date.now
     }
})

module.exports= mongoose.model('mytable',signUpTemplate) //two argument db name and schema name


come back to Router.js
 
 const express = require("express")
const router = express.Router()
const signUpTemplate= require('../models/backendsinghup')  //(new file)
 
 router.post('/signup', (request,response) =>{
const signupUser= new signUpTemplate({    // this will create new instance of SingupUser
    fullName:request.body.fullName,
    username:request.body.username,
    email:request.body.email,
    password:request.body.password
})
signupUser.save()
.then(data=>{   
response.json(data)
})
.catch(error =>{
    response.json(error)
}
    )
})

module.exports = router

----------------------------------------------------------------------
NOW GO TO MONGO DB.Create New project(Give Name to Project)

Then Create Cluster


Provide username and Password then click on Add User (username and password- demo). click on add my IP. Then click on Finish
Click on Database then click on connect then After Click on connect on Application

then copy that code - mongodb+srv://<username>:<password>@cluster0.vltnj.mongodb.net/myFirstDatabase?retryWrites=true&w=majority
Go back to Server.Js
Now connect application to Mongoo DB
Import Mongooes - const mongoose = require('mongoose')
mongoose.connect()// if we copy the code then we have to type username ans password here
Now safe way to do is create ENV package
Import Env Package
const dotenv = require('dotenv')
dotenv.config() //Activate ENV Package
create a new file called .env 
DATABASE_ACCESS="mongodb+srv://username:password@cluster0.vltnj.mongodb.net/DBName?retryWrites=true&w=majority"
now use env Package to access DataBase 
mongoose.connect(process.env.DATABASE_ACCESS,()=>console.log("Database Connected"))

Curently Route.Js file is Not connected to server.js file

copy this line in server.js
const routesUrls= require('./routes/route')


app.use('/app', routesUrls)

We needs to PassBody Passer for incoming and outgoing request
ap


Now you need install cors 
const cors = require('cors')
app.use(cors()) 

Lets Test Our Backend 

Now we will use API (Rest Client) for Best Our Backend

Click on View then Extension
Then Search Rest Client

Then create a file in same folder
test.http
POST http://localhost:4000/app/signup
Content-Type: application/json

{
    "fullName": "Rveen",
     "username":"Joe",
     "email":"pk@gmail.com",
     "password":"1234",
     "confirmpassword":"1234"
 
}


nodemon server.js

Now we have Successfully create a backend