DEV Community: Khushi

Server in Node JS

Khushi — Tue, 03 Jan 2023 11:51:55 +0000

A server listens to the incoming requests from a browser. Then it decides what will be its response to the client, in most cases, it is an HTML page, but it could be an image or CSS as well. How does a server identify what response should be sent?

IP Address

IP addresses are uniquely identified addresses to the computers which are connected to the internet. Some special computers known as Host means they host websites on the internet and publish a website. It will be hosted on the computer somewhere and all IP addresses to identify it and connect to it. They are a series of numbers, they could be hard to remember so we have a domain name to mask these IP addresses. When we type the domain in the browser and it will find the IP address associated with it and it will use that to find the computer that hosts the website, this way it can send requests and get back responses to and from it.

browser → Look-up IP address associated with the domain → Host

when we type something into the browser and hit enter that is a GET request. It s made every time we go to a different web page either by link or directly typing into the address bar.

Now this communication between the client and server happens via HTTPS (Hyper Text Transfer Protocol).

Local host

Localhost is like a domain name on the web but it takes us to a very specific IP address known as loopback IP address. That is 127.0.0.1 and it points to our own computer. We consider our computer as a host when we are developing the website.

Port Number

Port numbers are like a ‘door’ into a computer. It represents a gateway on our computer where a certain bit of software and server should communicate. There is software that interacts with the internet to receive and send data, but all of them has a different port number.

Creating a server

In Node , server are manually created which lives on the backend of our website.

Let s create a server that listens to the request and response to it.

const http = require('http')
const server = http.createServer((req,res)=>{
  console.log('request made');
})

server.listen(3000, 'localhost' , () =>{
    console.log(`listening for request at 3000`)
})

we use the http module to create a server. createServer method takes a callback with two arguments i.e. req(request) and res(response). Once we create a server, it listens to the requests, listen() method takes three arguments (port number, localhost, callback).

here it is! 🙂

Node JS Basics :)

Khushi — Mon, 02 Jan 2023 16:22:33 +0000

Difference between running JavaScript in Browser and Node JS

In the Brower if you do a right click and go to inspect

You will find the console where if we write window , we could see window object with different properties or method such as setTimeout() , setInterval() so we just have to write property name to use it. So the window object is global in the browser.

But in Node JS, we have global object with the keyword global so if we

console.log(global)

we get

now we write

global.setTimeout(() =>{
    console.log('in the timeout')
},3000)

we will get the desired output but since global is Global object so we don’t have to write global explicitly.

Two useful properties

console.log(__dirname) 
// absolute path of the current folder without current file 
console.log(__filename) 
// absolue path of the current folder with the current file

We can’t access DOM such as querySelector in global object in node.

Module and require

In text.js

const fruits = ['apple','mango','oranges','guava'];

console.log(fruits)

create a new JS file let say module.js and type

const xyz =  require('./text');

console.log(xyz)

it will give you result as

[ 'apple', 'mango', 'oranges', 'guava' ]
{}

xyz as no return value but if we add

const fruits = ['apple','mango','oranges','guava'];

console.log(fruits)

module.exports = fruits

then xyz will return
[ 'apple', 'mango', 'oranges', 'guava' ]

Another case would be if you want to export multiple values then

const fruits = ['apple','mango','oranges','guava'];
const age  = [1,2,3,4,5]
console.log(fruits)

module.exports = {
    fruits,
    age
}

now in module.js

const xyz =  require('./text');

console.log(xyz.age)

we also destructure it

const {people,age} =  require('./text');

console.log(age)

Node JS also contains core module such as OS, file system(fs) , etc.

const os = require('os')
console.log(os.homedir())

File System (fs)

It is used to handle files and perform operations such as reading, writing, deleting etc.

To import this

`const fs = require('fs');`

Destructure this

const {readFile,writeFile} = require('fs');

using this you don’t have to use ‘fs’ as a prefix before a method

→ Reading files

fs.readFile('./docs/path.txt',(err,data)=>{
  if(err)
  {
    console.log(err);
  }
  console.log(data);
})

this will give a buffer

Buffer is just a package of data that has been send towards when we read this file

so we have to convert data into string


  console.log(data.toString());

Also they are asynchronous means can start long-running tasks, and continue running other tasks in parallel*.*

→ Writing files

fs.writeFile('./docs/path.txt', 'hello , everyone' , () =>{
    console.log('file is wriiten');
})

It will overwrite the text in the file

→ Directories

if(!fs.existsSync('./assets')){ 
fs.mkdir('./assets',(err) =>{
    if(err){
        console.log(err);
    }
    else{
        console.log('folder created');
    }
})
}
else{
    fs.rmdir('./assets',(err) =>{
        if(err)
        {
            console.log(err);
        }
        console.log('folder deleted')
    })
}

if the directory doesn’t exists then it will be created using mkdir else it will be deleted using rmdir.

→ deleting files

//deleting files
if(fs.existsSync('./docs/delete.txt'))
{
    fs.unlink('./docs/delete.txt',(err) =>{
        if(err)
        {
            console.log(err);
        }
        console.log('file deleted')
    })
}

we use unlink method to delete the files

Streams and buffers

Now imagine we have a large data or file, we could wait for the file to be read completely but that could take a long time. We could pass the data in a bit of a Stream i.e. a small chunk of data that is known as a buffer and send down the stream every time a buffer fills so that you can start using the data. It is used for such as video loading.

Two types

Read streams and write streams

firstly,

const fs = require('fs');

const readStream = fs.createReadStream('./docs/path.txt', { encoding : 'utf8'});
const writeStream = fs.createWriteStream('./docs/path.txt',{flags : 'a'});

readStream.on('data',(chunk) =>{
     console.log('---New Chunk----');
     console.log(chunk);
     writeStream.write('---New Chunk----');
     writeStream.write(chunk);
 })

on is a event listener to listen to the buffer of data. ‘data’ is an event in this situation like ‘click’. In the above code after reading the buffer, it rewrites the buffer with 'writeStream'. To make the process short, we can just write*

readStream.pipe(writeStream)

that s it !🙂

reference - net ninja(youtube), coding addict(youtube), google search

Node JS Intro

Khushi — Wed, 28 Dec 2022 16:32:46 +0000

Node allows us to run JavaScript on the server side or directly on computers locally. A computer cannot directly understand JavaScript but it could be understood by the V8 engine in a browser. Node JS is written in C++. It can take JavaScript and run it to the V8 engine that is present in Node JS and compile it to the machine code.

It adds more functionality to the JavaScript➖

→ Read and write files on the computer

→ Connect to a database

→ Act as a server for content

but we can’t interact with DOM in Nodejs and Node JS doesn't support ES6 import directly.

Role of the Nodejs

Handling requests coming from the browser. Suppose a user might interact with your website and that browser sends a request to the server. Node JS will react to those requests, it might communicate with databases or files on a server and give a response to it, it could be an Html page embedded with data, image files, etc.

Why use Nodejs?

→ No need to learn an extra language for the server

→ can share code between front and backend

→ Nodejs has a massive community behind it

→ Huge amount of third-party packages and tools to help

after installing open any text editor

create a file text.js and type

const name = “Star”

console.log(name)

Now write in terminal “node text” and Enter

Your file will run

if you want to check the version of your node type

node -v

Here it is! node JS running in your system.

Reference : net ninja(YouTube)