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 NODE JS Definition:-

Node.js is an open-source and cross-platform javascript library that allows you to use JavaScript to develop server-side applications.


Every web browser has a JavaScript engine that takes JavaScript code and compiles it to machine code. For example, Firefox uses SpiderMonkey, and Google Chrome uses V8. Because browsers use different JavaScript engines, sometimes, you will see that JavaScript behaves differently between browsers.


In 2009, Ryan Dahl, the creator of Node.js, took the V8 engine and embedded it in an application that could execute JavaScript on the server.


Unique Features of NODE JS:-

Node.js is Single-threaded

Node.js is single-threaded. It means that each process has only one thread of execution.


The single-threaded execution model allows Node.js to handle more concurrent requests easily via the event loop. Because of this, Node.js applications typically consume comparatively less memory.


If you have not familiar with the event loop, check out this event loop tutorial. The event loop in Node.js works the same as the event loop in web browsers.


Node.js uses Non-blocking I/O

I/O stands for input/output. It can be disk access, a network request, or a database connection. I/O requests are expensive and slow and hence block other operations.

Node.js addresses blocking I/O issues by using non-blocking I/O requests.

Non-blocking means that you can make a request while doing something else, and then, when this request is finished, a callback will execute to handle the result.

In other words, the program execution can continue while other operations are taking place.


How to Install Node JS:-

Just write the download node in google it provides LTS , and download according to your o/s.

To confirm the installation, you can open Command Prompt or Windows Terminal and type the following command:


node -v


Step to create First Hello World Program in Node JS:-

1)  Create Folder

2) Open this folder in VS Code

3) Type npm init 

4) create hello.js file 

5) write following code

console.log("hello world")
6) open terminal write
node hello.js


What is Modules in NODE JS:-

It is similar to JS library, and it is used to contain predefine functionality under
NODE application.
We can create our own module also.
Node JS provide various modules, we will step all modules one by one


HTTP module in node js:-

This is the most important module to manage HttpRequest and HttpResonse.

Now I am creating one simple program to explain http module.

const http = require('http')
const hostname = '127.0.0.1'
const port = 3000
const server = http.createServer((req, res) => {
  res.statusCode = 200
  res.setHeader('Content-Type', 'text/html')
  res.end('<h1>Hello World</h1>')
})
server.listen(port, hostname, () => {
    console.log(`Server running at http://${hostname}:${port}/`)
  })

Another Example of an HTTP Module:-
const  http = require('http');

const port = 2000;
const host = "127.0.0.1"
const server = http.createServer((req,res)=>{
    res.statusCode=200
    var p = 120000
    var r = 5.5
    var t = 2
    var si = (p*r*t)/100
    res.setHeader('Content-Type','text/html')
    res.end(`<h1>Result is ${si} </h1>`)
})

server.listen(port,host,()=>{
    console.log(`click to execute http://${host}:${port}`)
})





Another Example of HttpModule:-

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <form action="http://127.0.0.1:3000/" method="get">
       <input type="text" name="txtnum1" placeholder="Enter First Number" />
       <br><br>
       <input type="text" name="txtnum2" placeholder="Enter First Number" />
       <br><br>
       <input type="submit" name="btnsubmit"  />

    </form>
</body>
</html>

Code for Add.js

var url = require('url');
const http = require('http')
const hostname = '127.0.0.1'
const port = 3000
const server = http.createServer((req, res) => {
//  console.log(req.url)
   var q = url.parse(req.url, true);
    var obj = q.query
    var res1 = parseInt(obj.txtnum1) + parseInt(obj.txtnum2)
    res.write(""+res1)
    res.end("<h1>Hello World</h1>")
  })
  server.listen(port, hostname, () => {
      console.log(`Server running at http://${hostname}:${port}/`)
    })

The HTTP module can create an HTTP server that listens to server ports and gives a response back to the client. using this we can create web server to post node script under web environment.
Use the createServer() method to create an HTTP server.


Read the query String using Http Module:-

 var http = require('http');
http.createServer(function (req, res) {
  res.writeHead(200, {'Content-Type': 'text/html'});
  res.write(req.url);
  res.end();
}).listen(8080);


File Module in Node JS:-

This is another important module in Node Js that is used to manage file operation.
1) Write File
2) Read File
3) Append File
4) Delete the File

This operation must be implemented using asynchronous mode

Now I am explaining using example:-

var fs = require('fs');
 fs.open('abc.txt', 'w', function (err, file) {
    if (err) throw err;
    console.log('Saved!');
  });
fs.writeFile('abc.txt', 'Hello content!', function (err) {
    if (err) throw err;
    console.log('Saved!');
  });
fs.readFile('abc.txt',(err, data) => {
    var array = data.toString().split(" ");
    console.log(data.toString());
    for(i in array) {
        // Printing the response array
        console.log(array[i]);
     }
 })

  fs.appendFile('abc.txt', ' dftrdyhtyt.', function (err) {
    if (err) throw err;
    console.log('Updated!');
  });
  fs.unlink('abc.txt', function (err) {
    if (err) throw err;
    console.log('File deleted!');
  });
  fs.rename('abc.txt', 'abcnew.txt', function (err) {
    if (err) throw err;
    console.log('File Renamed!');
  });
 
Example with Synchronous Operation:-

var data = fs.readFileSync('hello.txt');
console.log("Synchronous read: " + data.toString());


Node JS URL Module:-

The URL module splits up a web address into readable parts. To include the URL module, use the require() method.

Parse an address with the url.parse() method, and it will return a URL object with each part of the address as properties:

Now i am explaining url module using URL and Http Module Combination

var url = require('url');

const http = require('http')

const hostname = '127.0.0.1'

const port = 3000

const server = http.createServer((req, res) => {

//  console.log(req.url)

   var q = url.parse(req.url, true);

   

     console.log(q.host);

     console.log(q.pathname);

     console.log(q.search)

     console.log(q.query)

    res.end('<h1>Hello World</h1>')

  })

  server.listen(port, hostname, () => {

      console.log(`Server running at http://${hostname}:${port}/`)

    })


How to create NODE JS File Server:-

Using this we can create multiple files of Html and call using the NODE JS  Server with the help of HTTP and URL module.

Create home.html

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
</head>
<body>
<h1>Welcome in Home Page</h1>
</body>
</html>

create About.html

<!DOCTYPE html>
<html lang="en">
<head>
<title>Document</title>
</head>
<body>
<h1>Welcome in About us page</h1>
</body>
</html>

app.js

var http = require('http');
var url = require('url');
var fs = require('fs');
http.createServer(function (req, res) {
var q = url.parse(req.url, true);
console.log(q);
var filename = "." + q.pathname;
console.log(filename);
fs.readFile(filename, function(err, data) {
if (err) {
res.writeHead(404, {'Content-Type': 'text/html'});
return res.end("404 Not Found");
}
res.writeHead(200, {'Content-Type': 'text/html'});
res.write("<a href='./home.html'>Home</a>");
res.write("<a href='./about.html'>About us</a>");
res.write(data);
return res.end();
});
}).listen(8080);

Event Module in JS:-

This is very simple module that is used to perform the action, we can attach event dynamically using this Event Module.

var events = require('events');
var eventEmitter = new events.EventEmitter();
var fun = function(){
console.log("My User Define Event Method");
}
eventEmitter.on('myclick',fun);
eventEmitter.emit('myclick');

User Define Module:-

Using this we can create a custom module that can be used in another file.

Step 1st:-

Create Module:-

exports.mymodule = function () {
    return "Welcome in user define module";
  };

exports.fun = function () {
    return "module fun2";
  };

Use Module
const um = require('./mymodule')
console.log(um.mymodule())
console.log(um.fun())

What is Blocking & Non-Blocking of Code? NODE JS API supports the Non-Blocking of the code, it is a unique feature of the NODE JS Application and improves performance. Blocking of code means if one process is not completed then another process will be on hold but in non-blocking features if one process takes more time to execute then another process can be completed.
Example of Blocking of Code:-


var fs = require("fs");
var data = fs.readFileSync('hello.txt');
console.log(data.toString());
console.log("Program Ended");

Example of Non Blocking of Code:-

var fs = require("fs");

fs.readFile('hello.txt', function (err, data) {
   if (err) return console.error(err);
   console.log(data.toString());
});

console.log("Program Ended");

What is Stream?
Stream objects that is used to read data from source and write data into destination.

there are four types of streams − Readable − Stream which is used for read operation. Writable − Stream which is used for write operation. Duplex − Stream which can be used for both read and write operation. Transform − A type of duplex stream where the output is computed based on input.


The stream can be connected with Event Emitter instance and user various events to perform the operation

data − This event is fired when there is data is available to read. end − This event is fired when there is no more data to read. error − This event is fired when there is any error in receiving or writing data. finish − This event is fired when all the data has been flushed to underlying system.

Reading from Stream Example:-
var fs = require("fs");
var data = '';

// Create a readable stream
var readerStream = fs.createReadStream('hello.txt');

// Set the encoding to be utf8.
readerStream.setEncoding('UTF8');

// Handle stream events --> data, end, and error
readerStream.on('data', function(chunk) {
   data += chunk;
});

readerStream.on('end',function() {
   console.log(data);
});

readerStream.on('error', function(err) {
   console.log(err.stack);
});

console.log("Program Ended");

Writing data on Stream:-
var fs = require("fs");
var data = 'Simply Easy Learning';

// Create a writable stream
var writerStream = fs.createWriteStream('output.txt');

// Write the data to stream with encoding to be utf8
writerStream.write(data,'UTF8');

// Mark the end of file
writerStream.end();

// Handle stream events --> finish, and error
writerStream.on('finish', function() {
   console.log("Write completed.");
});

writerStream.on('error', function(err) {
   console.log(err.stack);
});

console.log("Program Ended");


How to connect NODE JS to Mongo DB:-
1) Install MONGODB IN Code
2) Type following command npm install mongodb
3) Create Following Code to perform Data Insertion Operation

var MongoClient = require('mongodb').MongoClient;
var url = "mongodb://localhost:27017/"
MongoClient.connect(url,function(err,db){
    if(err)
    throw console.error();
    var dbo = db.db("mydbnew");
    dbo.collection("students").insertOne({rno:1002,sname:"mno"},function(err,res){
        if(err)
        throw err
        console.log('data inserted successdfully')
    });
})


Create the Following Code for Data Selection:-

var MongoClient = require('mongodb').MongoClient;
var url = "mongodb://localhost:27017/";

MongoClient.connect(url, function(err, db) {
  if (err) throw err;
  var dbo = db.db("mydbnew");
  /*dbo.collection("students").findOne({}, function(err, result) {
    if (err) throw err;
    console.log(result.sname);
    db.close();
  });
});*/

dbo.collection("students").find({}).toArray(function(err, result) {
    if (err) throw err;
    console.log(result);
    db.close();
  });
});


Create Code for Data Updation:-

var MongoClient = require('mongodb').MongoClient;
var url = "mongodb://127.0.0.1:27017/";

MongoClient.connect(url, function(err, db) {
  if (err) throw err;
  var dbo = db.db("mydbnew");
  var myquery = { rno: 1001 };
  var newvalues = { $set: {sname: "Mickey"} };
  dbo.collection("students").updateOne(myquery, newvalues, function(err, res) {
    if (err) throw err;
    console.log("1 document updated");
    db.close();
  });
});


Create Code for Data Deletion:-

var MongoClient = require('mongodb').MongoClient;
var url = "mongodb://localhost:27017/";

MongoClient.connect(url, function(err, db) {
  if (err) throw err;
  var dbo = db.db("mydbnew");
  var myquery = { rno: 1001 };
  dbo.collection("students").deleteOne(myquery, function(err, obj) {
    if (err) throw err;
    console.log(" document deleted");
    db.close();
  });
});


Manage Join Operation in Node Js Project

1) First Create two Collection one for the Product and Another for the Order

Product Collection contains the productid, and product name, and Order collection contains orderid, productid, status

Write Following Example:-

var MongoClient = require('mongodb').MongoClient;
var url = "mongodb://127.0.0.1:27017/";

MongoClient.connect(url, function(err, db) {
  if (err) throw err;
  var dbo = db.db("mydbnew");
  dbo.collection('orders').aggregate([
    { $lookup:
       {
         from: 'products',
         localField: 'productid',
         foreignField: '_id',
         as: 'orderdetails'
       }
     }
    ]).toArray(function(err, res) {
    if (err) throw err;
    console.log(JSON.stringify(res));
    db.close();
  });
});

NODE JS API Example:-

Now I am providing the complete Example to create Restfull API in Node js

1) npm install express
2) npm install body-parser
3) npm install cors

const Express = require("express");
const BodyParser = require("body-parser");
const MongoClient = require("mongodb").MongoClient;
const ObjectId = require("mongodb").ObjectID;
const CONNECTION_URL ="mongodb://localhost:27017/" ;
const DATABASE_NAME = "mydbnew";
var app = Express();
var cors = require('cors')
app.use(cors())
app.use(BodyParser.json());
app.use(BodyParser.urlencoded({ extended: true }));
var database, collection;
app.listen(5000, () => {
    MongoClient.connect(CONNECTION_URL, { useNewUrlParser: true }, (error, client) => {
        if(error) {
            throw error;
        }
        database = client.db(DATABASE_NAME);
        collection = database.collection("students");
        console.log("Connected to `" + DATABASE_NAME + "`!");
    });

});
app.get("/studata", (request, response) => {
    collection.find({}).toArray((error, result) => {
        if(error) {
            return response.status(500).send(error);
        }
        response.send(result);
    });
});

app.get("/stu/:id", (request, response) => {
    collection.findOne({ "_id": new ObjectId(request.params.id) }, (error, result) => {
        if(error) {
            return response.status(500).send(error);
        }
        response.send(result);
    });
});


app.post("/studata", (request, response) => {
    collection.insert(request.body, (error, result) => {
        if(error) {
            return response.status(500).send(error);
        }
        response.send(result.result);
    });
});

app.put("/stu/:id", (request, response) => {
    collection.updateOne({ "_id": new ObjectId(request.params.id) },{$set:request.body}, (error, result) => {
        if(error) {
            return response.status(500).send(error);
        }
        response.send(result.result);
    });
});
app.delete("/stu/:id", (request, response) => {
    collection.remove({ "_id": new ObjectId(request.params.id) }, (error, result) => {
        if(error) {
            return response.status(500).send(error);
        }
        response.send(result);
    });
});






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