Forem: Chandra Prakash Pal

Recursion

Chandra Prakash Pal — Thu, 11 Sep 2025 12:57:11 +0000

What is Recursion?

Recursion is a programming technique where a function calls itself to solve smaller instances of a problem until it reaches a base case (a stopping condition). It's widely used for problems that can be broken down into similar sub-problems.

Real-Life Example of Recursion

Example: Russian Dolls (Matryoshka Dolls)

Imagine you have a set of Russian dolls, each nested inside a larger one.

To open all dolls:

You open the outermost doll.
Inside, you find another doll and repeat the process.
You stop when you find the smallest doll, which doesn’t contain any more dolls.

This mimics recursion:

Recursive Step: Open the next doll (function calls itself).
Base Case: The smallest doll (no more dolls inside).

Tips and Tricks for Solving Problems Using Recursion

Identify the Base Case
- The base case is the simplest version of the problem where recursion will stop.
- Without a base case, recursion leads to infinite loops or stack overflow.
Break Down the Problem
- Divide the problem into smaller, similar sub-problems.
- Each recursive call should work on a smaller input.
Think in Terms of “What’s Left to Do?”
- What part of the problem can you handle now, and what can you delegate to future recursive calls?
Avoid Redundant Calculations
- Use memoization or dynamic programming for optimization: store results of sub-problems to avoid re-computation.
Understand Stack Limitations
- Recursive calls use the call stack. Deep recursions can lead to stack overflows. Iterative solutions may be preferred in such cases.
Test with Small Inputs
- Debug your recursion logic with simple and small inputs to verify base case and recursive steps.

Must Applicable Conditions for Using Recursion

Problem Can Be Divided into Similar Sub-Problems: E.g., tree traversal, factorial calculation, Fibonacci sequence.
Base Case Exists: There is a clear condition to stop further recursive calls.
Sub-Problems Are Independent: Recursive calls do not interfere with each other’s results.
Recursive Solution Is More Elegant or Simpler than Iterative: Some problems are naturally recursive (e.g., traversing hierarchical data).

Example in Code: Factorial

function factorial(n){
    # Base case
    if n == 0:
        return 1
    # Recursive case
    return n * factorial(n - 1)
}

Summary:

Recursion works best when problems are self-similar and have a clear stopping point. Always ensure a base case, break the problem down, and watch out for performance and stack limitations. Use recursion when it makes your code cleaner, simpler, and easier to understand!

Nested category example

const AllCategories = [
  {
    id: 1,
    name: 'Electronics',
    children: [
      {
        id: 2,
        name: 'Mobile Phones',
        children: [
          {
            id: 3,
            name: 'Smartphones',
            children: [],
          },
          {
            id: 4,
            name: 'Feature Phones',
            children: [],
          },
        ],
      },
      {
        id: 5,
        name: 'Laptops',
        children: [],
      },
    ],
  },
  {
    id: 6,
    name: 'Home Appliances',
    children: [],
  },
];

async function processCategory(categories) {
  let result = [];
  for (const category of categories) {
    const product_count=1
    let childrenWithCount=[]
    if(category.children && category.children.length>0){
        childrenWithCount=await processCategory(category.children)
    }
    result.push({ ...category, product_count,children:childrenWithCount });
  }
  return result
}
processCategory(AllCategories)
  .then(result => {
    console.log(JSON.stringify(result));
  })
  .catch(error => {
    console.log(error);
  });

Result

[
  {
    "id": 1,
    "name": "Electronics",
    "children": [
      {
        "id": 2,
        "name": "Mobile Phones",
        "children": [
          {
            "id": 3,
            "name": "Smartphones",
            "children": [],
            "product_count": 1
          },
          {
            "id": 4,
            "name": "Feature Phones",
            "children": [],
            "product_count": 1
          }
        ],
        "product_count": 1
      },
      {
        "id": 5,
        "name": "Laptops",
        "children": [],
        "product_count": 1
      }
    ],
    "product_count": 1
  },
  {
    "id": 6,
    "name": "Home Appliances",
    "children": [],
    "product_count": 1
  }
]

Microservices Architecture

Chandra Prakash Pal — Thu, 19 Jun 2025 08:03:53 +0000

Great! Let’s go step-by-step and thoroughly understand Microservices architecture from the perspective of a Node.js backend developer. I'll explain:

🔍 1. What is Microservices Architecture?

Microservices is an architectural style where an application is divided into a set of loosely coupled, independently deployable services, each handling a specific business capability.

Instead of building one large monolithic application, you break it into small services that communicate over a network.

🏗 Example: eCommerce Platform

Let’s compare Monolith vs Microservices.

🔸 Monolithic App

A single codebase and server handles:

User Authentication

Product Catalog

Orders

Payments

Admin Panel

If something crashes, the whole app fails.

🔸 Microservices App

Each service is a separate app:

Microservice Responsibility Port / DB Language

user-service Login, register, profile MongoDB Node.js
product-service Catalog management PostgreSQL Go
order-service Order placement, status MySQL Node.js
payment-service Payments, refunds Redis Python

Services communicate over the network (TCP/HTTP/gRPC/RabbitMQ/etc).

🧩 2. Key Characteristics

Feature Description

Independent Deploys Each service can be deployed separately
Polyglot Use different languages, databases
Resilience One service failure doesn’t crash the entire app
Scalability Scale only the heavy-loaded services
DevOps Friendly CI/CD is easier with small units

🔌 3. Communication Methods Between Services

There are multiple inter-service communication mechanisms:

Method Description Example Use

HTTP REST Simple APIs over HTTP API Gateway to Microservice
TCP Fast, persistent connections NestJS TCP transport
gRPC Binary, performant RPC calls Real-time apps
Message Bus RabbitMQ / Kafka / NATS Event-driven architecture
WebSockets Bidirectional live connections Chat / real-time systems

🧭 4. What is an API Gateway in Microservices?

An API Gateway is a single entry point for clients to interact with microservices.

🧱 Role of API Gateway

Feature Description

Routing Directs client requests to appropriate services
Aggregation Combines data from multiple services
Security Handles authentication, rate-limiting
Logging/Monitoring Logs requests and errors
Versioning API version control

🔁 Real-World Example

Request: GET /orders

API Gateway:

Validates JWT

Forwards to order-service

Fetches user details from user-service

Merges both

Sends single response to frontend

🧰 5. Do I Build the Gateway or Use Third-Party?

✅ Option 1: Build Your Own (recommended for control/custom logic)

Use:

NestJS with HTTP + TCP clients

Express.js

Fastify

Pros:

Full control

Tailor-made logic

Cons:

You manage load balancing, security, rate-limiting manually

✅ Option 2: Use API Gateway Providers (recommended for production-scale infra)

Gateway Features

Kong Open source, plugins, rate limit, auth
NGINX Lightweight, reverse proxy
AWS API Gateway Fully managed, serverless
Traefik Auto-routing with Docker/K8s
Istio (K8s) Advanced service mesh with observability

Note: These tools often integrate with service discovery (e.g., Consul, Eureka) in large setups.

🏗 6. Development Methodologies for Microservices

There are several ways to design and build microservices:

🔹 A. REST-based Microservices

Services communicate over REST APIs

Lightweight and easy to debug

Ideal for basic CRUD services

🔹 B. Event-Driven Microservices

Communicate via events (Kafka, RabbitMQ, NATS)

Services publish/subscribe events

Useful for loosely coupled and scalable systems

Example: order-service emits order_placed → payment-service listens to it

🔹 C. RPC-based Microservices (TCP/gRPC)

Services talk over Remote Procedure Calls

High performance

Often used in NestJS (TCP) or gRPC (Google)

🧪 Example Architecture in NestJS

Communication: REST → Gateway → TCP (NestJS transport) between services.

✅ Summary

Topic Key Point

Microservices Split app into small, independent services
Communication Use TCP, REST, gRPC, or Messaging
API Gateway Front door to your services
Build vs Buy Gateway You can build (NestJS) or use Kong, AWS
Development Styles REST-based, Event-driven, RPC
NestJS Support Built-in support for TCP/gRPC/RMQ/Kafka microservices

Would you like to:

Learn Event-Driven architecture next
Learn gRPC vs TCP vs REST comparison
Set up a message broker (like RabbitMQ) in your microservice system
Learn about Service Discovery and dynamic microservices registration?

Let me know!

https://zenduty.com/blog/observability-tools/

Chandra Prakash Pal — Mon, 09 Jun 2025 22:43:06 +0000

Use async await with Array.map

Chandra Prakash Pal — Wed, 02 Apr 2025 16:45:29 +0000

Problem Context:

var arr = [1,2,3,4,5];

var results: number[] = await arr.map(async (item): Promise<number> => {
        await callAsynchronousOperation(item);
        return item + 1;
    });

Error Context:
TS2322: Type 'Promise[]' is not assignable to type 'number[]'. Type 'Promise is not assignable to type 'number'.

Solution Context:

The problem here is that you are trying to await an array of promises rather than a Promise. This doesn't do what you expect.

When the object passed to await is not a Promise, await simply returns the value as-is immediately instead of trying to resolve it. So since you passed await an array (of Promise objects) here instead of a Promise, the value returned by await is simply that array, which is of type Promise[].

What you probably want to do is call Promise.all on the array returned by map in order to convert it to a single Promise before awaiting it.

var arr = [1, 2, 3, 4, 5];

var results: number[] = await Promise.all(arr.map(async (item): Promise<number> => {
    await callAsynchronousOperation(item);
    return item + 1;
}));

Javascript how to check object is empty or not

Chandra Prakash Pal — Mon, 15 Jul 2024 04:09:24 +0000

In JavaScript everything start with object. Object has vital role while working with JavaScript.

We define object with two curly braces like

const user={}; later can add key value pairs in it like user.name="User" user.email="user@gmail.com"

But mostly we have to check that object is empty or not. So let's check it

const user={};

console.log(Object.keys(user).length) // will log 0

user.name="User" user.email="user@gmail.com" console.log(Object.keys(user).length) // will log 2

Deploy NodeJs Application On Ubuntu and Nginx

Chandra Prakash Pal — Fri, 21 Jun 2024 09:21:08 +0000

When using the Nginx web server, server blocks (similar to virtual hosts in Apache) can be used to encapsulate configuration details and host more than one domain on a single server.

In this guide, we’ll discuss how to configure server blocks in Nginx on an Ubuntu.

Login on remote machine by ssh

First login on remote machine by ssh as follows

ssh user@remote_ip

After login on remote install nodejs on machine, if already installed then ignore it.

You can check installation guide from here

Clone your project from Github

There are a few ways to get your files on to the server, I would suggest using Git

git clone yourproject.git

Install dependencies and test app

`cd yourproject
npm install
npm start (or whatever your start command)

stop app

ctrl+C`

Setup ufw firewall

sudo ufw enable
sudo ufw status
sudo ufw allow ssh (Port 22)
sudo ufw allow http (Port 80)
sudo ufw allow https (Port 443)

Install NGINX and configure

sudo apt install nginx

sudo nano /etc/nginx/sites-available/default

Add the following to the location part of the server block

`server {
server_name your_domain www.your_domain;
location / {
proxy_pass http://localhost:3000;
proxy_http_version 1.1;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection 'upgrade';
proxy_set_header Host $host;
proxy_cache_bypass $http_upgrade;
}

`# Check NGINX config
sudo nginx -t

Restart NGINX

sudo service nginx restart`

Make the symbolik linking by running following

sudo ln -s /etc/nginx/sites-available/{your_domain or folder name in sites_availabe}/etc/nginx/sites-enabled

Secure Nginx with Let's Encrypt

Let’s Encrypt is a Certificate Authority (CA) that provides an easy way to obtain and install free TLS/SSL certificates, thereby enabling encrypted HTTPS on web servers. It simplifies the process by providing a software client, Certbot, that attempts to automate most (if not all) of the required steps.

Installing Certbot

sudo apt install certbot python3-certbot-nginx

Confirming Nginx’s Configuration

To check, open the configuration file for your domain using nano or your favorite text editor:

sudo nano /etc/nginx/sites-available/example.com

Find the existing server_name line. It should look like this:

/etc/nginx/sites-available/example.com
...
server_name example.com www.example.com;
...

If it does, exit your editor and move on to the next step.

verify the syntax of your configuration file

sudo nginx -t

Once your configuration file’s syntax is correct, reload Nginx to load the new configuration:

sudo systemctl reload nginx

Obtaining an SSL Certificate

sudo certbot --nginx -d example.com -d www.example.com

Credits goes to following references

NodeJS App Deployment On Ubuntu Server

How To Set Up a Node.js Application for Production on Ubuntu 20.04

How To Secure Nginx with Let's Encrypt on Ubuntu

Create virtual host on nginx server(Ubuntu)

Chandra Prakash Pal — Thu, 20 Jun 2024 08:30:34 +0000

The deployment of application on server is a very tedious task. From installation of nginx to creation of virtual host and linking of virtual host from /etc/nginx/sites-available to /etc/nginx/sites-ebabled. Without the enable of virtual host will not work.

Following are steps to create virtual host and make it enabled to work.

create a host file on location /etc/nginx/sites-available/{your_host_file}
Ex. /etc/nginx/sites-available/demo-app
Next add the following code in host file

server { location / { proxy_pass http://localhost:4100; proxy_http_version 1.1; proxy_set_header Upgrade $http_upgrade; proxy_set_header Connection 'upgrade'; proxy_set_header Host $host; proxy_cache_bypass $http_upgrade; } }

Now enable the host by following commnad

sudo ln -s /etc/nginx/sites-available/demo-app /etc/nginx/sites-enabled/

PM2 Add NodeJs Project In Process List

Chandra Prakash Pal — Fri, 14 Jun 2024 13:44:10 +0000

During the NodeJs project deployment we use the PM2 as process manager.

PM2 monitor the application and restart it automatically while if app is crashing.

First install PM2 package

`$ npm install pm2@latest -g

or

$ yarn global add pm2`

When managing multiple applications with PM2, use a JS configuration file to organize them.

To generate a sample configuration file you can type this command:

pm2 init simple

This will generate a sample ecosystem.config.js:

module.exports = { apps : [{ name : "app1", script : "./app.js" }] }

Now the command to add NodeJs project in pm2 list with npm script are following way

pm2 start npm --name "{project_name}" -- run {script_name}

For Example ,let's i have a project with name HelloWorld and script to run the project are npm run dev the following command will be.

pm2 start npm --name "rStoreFront Backend" -- run dev

Here are some references for deploy nodejs project

How To Set Up Nginx Server Blocks (Virtual Hosts) on Ubuntu 16.04

https://www.digitalocean.com/community/tutorials/how-to-set-up-a-node-js-application-for-production-on-ubuntu-18-04

How To Set Up a Node.js Application for Production on Ubuntu 20.04

Javascript expression execution order

Chandra Prakash Pal — Wed, 12 Jun 2024 15:46:24 +0000

JavaScript always evaluates expressions in strictly left-to-right order.

In general, JavaScript expressions are evaluated in the following order:

Parentheses
Exponents
Multiplication and division
Addition and subtraction
Relational operators
Equality operators
Logical AND
Logical OR

It is important to understand the order in which expressions are evaluated in order to write code that works correctly.

Here are the most commonly used operators in JavaScript, ordered by precedence from highest to lowest:

Grouping: ()
Unary: +, -, !
Multiplicative: *,/, %
Additive: +, -
Relational: <, >, <=, >=
Equality: ==, != , ===, !==
Logical AND: &&
Logical OR: ||

Reference taken from here

Javascript wait inside loop for complete asynchronous task in synchronous way.

Chandra Prakash Pal — Mon, 03 Jun 2024 08:24:37 +0000

Get Reference from here.

Differences between CSS transitions, transforms, and animations

Chandra Prakash Pal — Sat, 11 May 2024 13:38:28 +0000

Here are some differences between CSS transitions, transforms, and animations:
Transitions
Transitions are state changes that move from one state to another, like a :hover state. They require a trigger to run, and they run forwards when triggered and in reverse when the trigger is removed. Transitions have properties for the name of the property, the duration, any delay, and timing functions.
Transforms
Transforms change the shape and position of content by modifying the coordinate space. They can rotate, move, skew, and scale elements.
Animations
Animations can have multiple stages and are better for more complex movements. They don't require a trigger to run, and they can be played forwards, backwards, or in alternate cycles. Animations have the same properties as transitions, but with the word "animation" instead of "transition".

Random Password Generate

Chandra Prakash Pal — Wed, 24 Apr 2024 05:55:45 +0000

When we develop any application, we need a random password for every user.As more as secure password is recommended. The conditions for secure password must follow

Minimum 8 character long password
Minimum one uppercase letter
Minimum one lowercase letter
Minimum one special character
Minimum one number.

The combination of above condition will generate a secure password.

function generatePassword(length) {
    // code to generate passowrd
    var charNum = "0123456789";
    var charLower = "abcdefghijklmnopqrstuvwxyz"
    var charUpper = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
    var charSpecial = "!@#$%^&*_"
    var charAll = charNum + charLower + charUpper + charSpecial;
    var password = "";
    for (var i = 0; i < length; i++) {
        if (i == 0) {
            password += charUpper.charAt(Math.floor(Math.random() * charUpper.length));
        }
        if(i == 1){
            password += charLower.charAt(Math.floor(Math.random() * charLower.length));
        }
        if(i == 2){
            password += charNum.charAt(Math.floor(Math.random() * charNum.length));
        }
        if(i == 3){
            password += charSpecial.charAt(Math.floor(Math.random() * charSpecial.length));
        }
        var char = charAll[Math.floor(Math.random() * charAll.length)];
        password += char;
    }
    return password;
}