DEV Community: Raghul

PostgreSQL-2

Raghul — Mon, 10 Aug 2026 08:42:04 +0000

PostgreSQL

In database create table called employee.
create table employee(empid integer, name varchar(25), designation varchar(25),dept varchar(25), salary integer);

insert
insert into employee values(123,'Kavin','SoftwareEngineer','DB',25000);
insert into employee values(124, 'Viyan', 'Software Engineer', 'AI',27000);

Add more rows in single insert statement:
insert into employee values(101, 'Arul', 'Team Lead', 'Front End', 35000), (101, 'Agaran', 'Team Lead', 'DB', 45000);

Change Table Name:
alter table employee rename to employees;

Select:
Using distinct to get unique values
select distinct designation from employees;

where clause:
select * from employees where dept = 'DB';

where, and
select * from employees where dept =’DEV’ and designation = ‘Manager’;

where, or:
select * from employees where dept = ‘’ or designation = ‘’;

as:
select dept as department from employees;
to show the name as we want

Not Equals to:

select * from employees where dept <> ‘DB’;
select * from employees where dept != ‘DB’;
select * from employees where not dept = ‘DB’;

> greater than:
select * from employees where salary > 28000;

between:
select * from employees where salary between 19000 and 35000;

in
select * from employees where dept in('DB','DEV');

and
select * from employees where name ='Kavin' and dept ='DB';

or
select * from employees where name ='Kavin' or dept ='DB';

order by
select * from employees order by dept;(ascending order)
select * from employees order by dept desc;

limit
select * from employees order by salary limit 3;
give first 3 values
select * from employees order by salary desc limit 3;
give lasr 3 values

LIKE Operator
select * from employees where name like ‘A%’;
select * from employees where name like ‘%A%’;

super whoooooo

Raghul — Mon, 10 Aug 2026 06:15:30 +0000

Raghul

Aug 10

SQL-1

#srnsql #sql #postgres #beginners

3 min read

Database

Raghul — Mon, 10 Aug 2026 06:12:46 +0000

Database

Databases is a digital repository essential for storing, retrieving, and managing structured or unstructured data.

They form the backbone of modern applications—from mobile apps to enterprise systems.
The choice of database impacts performance, scalability, consistency, and data integrity.
Databases are classified based on structure, data model, storage method, and use case.

Type of Database(TBD)
Organizations use different types of databases to manage different types of data and support different applications. Some of the most
common types of databases include:

1. Hierarchical Databases
Hierarchical databases organize data in a tree-like structure, where each parent record can have multiple child records. This model works well for scenarios where data follows a predefined hierarchical relationship, where data is arranged in levels or ranks. To reach the wanted record, users must start at the top of the tree and work their way down.

For example, in a university, "University" is at the top level, while "Departments" and "Administration" are at lower levels, even though they are distinct entities. This structure can also be viewed as a parent-child relationship, where each parent record can have multiple child records, but a child record can only have one parent. As more data are added, the structure expands like a tree.
Example:

IBM's Information Management System (IMS).
Operating System File Systems: Your computer's hard drive uses this model. A single root directory (C:\ or /) acts as the top parent, containing subfolders (child nodes) which hold individual file.
XML and HTML Documents: Data format models like XML organize data via tags into strict parent-child hierarchies. A tag acts as a parent containing multiple child tags.
The Windows Registry: Windows operating systems use a hierarchical database to store configuration settings. It organizes keys and subkeys into a strict nested tree structure.

2. Network Databases
A network databases build on the hierarchical model but allow child records to be linked to multiple parent records, creating a web-like structure of interconnected data. This results in a more flexible structure, often referred to as a graph model, where entities can be connected in many different ways.

For example: club<---->students. In a University database, a student can join multiple clubs and a club can have multiple students. This model is ideal for complex frameworks as it effectively represents many-to-many relationships. Additionally, its structure simplifies the use of certain database management languages.
Examples:

The Integrated Data Store (IDS) is a well-known example of a network database.
University Course System: A single student can enroll in multiple courses (parents), and a single course contains multiple students.
Store Inventory: An item can be supplied by multiple vendors, and a single vendor can supply multiple different items.
Company Project Staffing: An employee can work on multiple projects simultaneously, and each project consists of multiple team members.

3. Object-Oriented Databases
Object-oriented databases are based on the principles of object-oriented programming (OOP), where data is stored as objects. These objects include attributes (data) and methods (functions), making them easily referenced and manipulated. These databases are designed to handle complex data structures such as multimedia, graphics, and large files. Object-oriented databases are especially useful for applications involving complex data types or multimedia content.

For instance, a "Person" object in the database could include attributes like Name and Address and methods like getLatestAddress() to retrieve information. This approach reduces the workload on the database by allowing objects to be reused and linked directly, streamlining data access and manipulation. Each object behaves as an instance of thedatabase model, enabling efficient operations.
A practical example of this model is the Berkeley DB software library, which is designed for fast and efficient query responses in embedded systems.
4. Relational Databases
Relational databases are the most widely used type of database today. They store data in tables, with rows representing records and columns representing attributes of the records. In these databases, every piece of information has a relationship with every other piece of information. This is on account of every data value in the database having a unique identity in the form of a record. Note that all the data are tabulated in this model.

Therefore, every row of data in the database is linked with another row using a primary key. Similarly, every table is linked with another table using a foreign key. Refer to the diagram below and notice how the concept of 'Keys' is used to link two tables.

Due to this introduction of tables to organize data, it has become exceedingly popular. In consequence, they are widely integrated into Web-App interfaces to serve as ideal repositories for user data.

What makes it further interesting is the ease in mastering it, since the language used to interact with the database is simple (SQL in this case) and easy to comprehend. In Relational databases, scaling and traversing through data is quite a lightweight task in comparison to Hierarchical Databases.

Example: MySQL, PostgreSQL, and Oracle Database are some popular relational databases.

5. Cloud Databases (TBD)
A cloud database operates in a virtual environment hosted on cloud computing platforms. It is designed for storing, managing, and executing data over the internet, providing flexibility and scalability. Cloud databases are widely used for applications requiring dynamic workloads, as they eliminate the need for on-premises infrastructure.

Common cloud services for accessing and managing databases include SaaS (Software as a Service) and PaaS (Platform as a Service), which simplify database operations for businesses. Popular cloud platforms offering database services include:

Amazon Web Services (AWS)
Google Cloud Platform (GCP)
Microsoft Azure
ScienceSoft, etc.

6. NoSQL Databases
A NoSQL database (short for "non-SQL" or "non-relational") provides a mechanism for storing and retrieving data that does not rely on traditional table-based relational models. Instead, it uses flexible data models like key-value pairs, documents, column families, or graphs, making it ideal for handling unstructured, semi-structured, and structured data.

NoSQL databases are known for their simplicity of design, horizontal scalability (adding more servers for scaling), and high availability. Unlike relational databases, their data structures allow faster operations in certain use cases. MongoDB, for instance, is a widely used document-based NoSQL database and other are redis Apache cassandra.

Real World Application of Database
Databases are used in most modern applications, whether the database is on our personal phone, computer or the internet. An operational database system will store much of the data an application needs to function, keeping the data organized and allowing users to access the data.
If an eCommerce application was created, there will be some data that the application would access and store in the operational database system, such as:

Customer data: like usernames, email addresses, and preferences, and etc.
Business data: like product properties, prices, reviews and ratings, , and etc.
Relationship data: a customer can view multiple products, and vice versa.

SQL-1

Raghul — Mon, 10 Aug 2026 06:09:28 +0000

SQL

Structured Query Language (SQL) is the standard language used to interact with relational.

SQL is a standard language for storing, manipulating and retrieving data in databases.
Mainly used to manage data. Whether you want to create, delete, update or read data, SQL provides commands to perform these operations.
Widely supported across various database systems like MySQL oracle, PostgreSQL, SQL Server and many others.
Mainly works with Relational Databases (data is stored in the form of tables).

There are many Relational Database Management Systems (RDBMS) that run on SQL but mainly:

MySQL: The world's most popular open-source database, powering major websites like WordPress, Facebook, and YouTube due to its speed and simplicity.
PostgreSQL: Known as the most advanced open-source database, favored by developers for complex data types, heavy writing operations, and enterprise features.
SQLite: A tiny, serverless database embedded directly inside nearly every smartphone, web browser, and desktop application on earth.

Log files
Log files are typically stored as plain text (.log, .txt), JSON, or CSV formats, recording a time-stamped chronological list of system or application events. You can read small logs using basic text editors or large logs using specialized command-line tools and viewers.

PostgreSQL

PostgreSQL is a free open-source database system that supports both relational (SQL) and non-relational (JSON) queries and extends the SQL language combined with many features that safely store and scale the most complicated data workloads. It is a back-end database for dynamic websites and web applications.

Why we want PostgreSQL
PostgreSQL comes with many features aimed to help developers build applications, administrators to protect data integrity and build fault-tolerant environments, and help you manage your data no matter how big or small the dataset. In addition to being free and open source, PostgreSQL is highly extensible. For example, you can define your own data types, build out custom functions, even write code from different programming languages without recompiling your database.

To open it

sudo -i -u postgres

sudo: super user do
i: Start a login shell. [Loading the User’s Environment automatically]
u: user
postgres: username
Why do we use it?
When PostgreSQL is installed, it creates a special Linux user called postgres.
This user:
• Owns the PostgreSQL server process.
• Has permission to administer PostgreSQL.
• Can connect to the database using peer authentication without entering a database password.

psql
Then type psql it is the interactive command-line client for PostgreSQL. It allows you to connect to a PostgreSQL server, execute SQL queries, create databases and tables,
and administer the database.

Some basic function
\l-To list all databases.
\h-To help.
\r-To stop or recover.
\c-To connect to database or table.

create database Movie;
By this we can create database.

\c movie or psql movie
To Connect to newly created database.

select version();
To know version of postgres.

select current_date;
To know current date.

Now we can learn SQL with PostgreSQL

Create Table:
create table movie
(
movie_name varchar(80),
release_date date,
ticket int
);

Note:

Two dashes (“--”) introduce comments. Whatever follows them is ignored up to the end of the line.
SQL is case insensitive about key words and identifiers, except when identifiers are double-quoted to preserve the case (not done above).

Datatypes:

1) varchar, char
2) int, smallint, numeric
3) real, double
4) date, time, timestamp
5) point [postgresql specific datatype]

Populating a Table with rows:
insert- insert into movie values('jananayagan','2026-07-15', 120);
insert into movie (release_date, movie_name, ticket) values ('2025-01-10','sirai',120);
insert into movie(movie_name, ticket) values ('karuppu',120);

select * from movie; or select movie_name, release_date, ticket from movie;
here * universal selector select all table

Select movie_name, release_date, ticket*4 as family_price from movie;
it show the value by perform this multiplication function.

Python

Raghul — Mon, 10 Aug 2026 05:58:24 +0000

Python Introduction

Python is a popular and simple programming language. It was created by Guido van Rossum, and released in 1991 as Python 0.9.0. Python 2.0 was released on 16 October 2000, featuring many new features such as list comprehensions, cycle-detecting garbage collection, reference counting, and Unicode support[TBD]. Python 2.7's end-of-life because it's backward incompatible and was initially set for 2015, and then postponed to 2020 out of concern that a large body of existing code could not easily be forward-ported to Python 3.[50][51] It no longer receives security patches or updates.

Python Shell

A Python shell is an interactive user interface that lets you type Python code and see results right away.
To open:
Type python3 on terminal to open directly.
Now you will see >>> so now we can

JavaScript Array Iteration Methods

Raghul — Mon, 20 Jul 2026 16:16:35 +0000

JavaScript Array Iteration Methods

JavaScript Array iteration methods perform some operation on each element of an array. Array iteration means accessing each element of an array. JavaScript provides mainly 3 simple statements for looping over each array items.

for ... of (loops over entries)
for ... in (loops over indexes)
forEach (myFunction)

1.The for...of Loop
The for...of statements hands you the array values.

// Create an Array
const cars = ['BMW', 'Volvo', 'Mini'];

// Iterate over the Array values
let text = "";
for (let x of cars) {
  text += x + ",";
}

2.The for...in Loop
The for...in statements hands you the array indexes. To make it return the elements you must use [x]. for...in was created to inspect Object properties (like: name, age, height), not Arrays.

// Create an Array
const cars = ['BMW', 'Volvo', 'Mini'];

// Iterate over the Array values
let text = "";
for (let x in cars) {
  text += x + ",";
}

// Create an Array
const cars = ['BMW', 'Volvo', 'Mini'];

// Iterate over the Array values
let text = "";
for (let cars[x] in cars) {
  text += x + ",";
}

3.JavaScript Array forEach()
The forEach() method calls a function (a callback function) for each array element. The provided function is user-defined, it can perform any kind of operation on an array.
Syntax:

array.forEach(function callback(value, index, array) {
} [ThisArgument]);

Parameters: This function accepts three parameters as mentioned above and described

value: This is the current value being processed by the
index: The item index is the index of the current element which was being processed by the
array: The array on which the .forEach() method was called.

let emptytxt = "";
let  Arr = [23, 212, 9, 628, 22314];

function itrtFunction(value, index, array) {
    console.log(value);
}

Arr.forEach(itrtFunction);
//output 
23
212
9
628
22314 //

4.JavaScript Array map()
The array.map() method creates an array by calling a specific function on each item in the parent array and it does not change the value or element of the array. It does not execute the function for array elements without values.
Syntax:

array.map(function(value, index, array){
}[ThisArgument]);

Parameters: This method accepts three parameters as mentioned above and described

value: This is the current value being processed by the
index: The item index is the index of the current element which was being processed by the
array: The array on which the .map() function was called.

const numbers1 = [45, 4, 9, 16, 25];
const numbers2 = numbers1.map(myFunction);

function myFunction(value, index, array) {
  return value * 2;
}

Array Methods in JavaScript

Raghul — Thu, 16 Jul 2026 15:41:50 +0000

Array Methods in JavaScript

To help you perform common tasks efficiently, JavaScript provides a wide variety of array methods. These methods allow you to add, remove, find, and transform array elements with ease.v

1. JavaScript Array length
The length property of an array returns the number of elements in the array. It automatically updates as elements are added or removed. The length property can also be used to set the length of an array.

let a = ["HTML", "CSS", "JS", "React"];
console.log(a.length);

// to set the length of an array
const fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.length = 2;

2. JavaScript Array toString() Method
The toString() method converts the given value into the string with each element separated by commas. Every JavaScript object has a toString() method. The toString() method is used internally by JavaScript when an object needs to be displayed as a text (like in HTML), or when an object needs to be used as a string.

let a  = ["HTML", "CSS", "JS", "React"];
let s = a.toString();
console.log(s);

3. JavaScript Array join() Method
This join() method creates and returns a new string by concatenating all elements of an array. It uses a specified separator between each element in the resulting string. It behaves just like toString(), but in addition you can specify the separator.

let a = ["HTML", "CSS", "JS", "React"];
console.log(a.join('|'));

4.JavaScript Array at()
ES2022 introduced the array method at(). The at() method returns an indexed element from an array. The at() method returns the same as []. Many languages allow negative bracket indexing like [-1] to access elements from the end of an object / array / string. This is not possible in JavaScript, because [] is used for accessing both arrays and objects. obj[-1] refers to the value of key -1, not to the last property of the object. So to solve this the at() method was introduced in ES2022.

const fruits = ["Banana", "Orange", "Apple", "Mango"];
let fruit = fruits.at(-2);

5.JavaScript Array.pop() Method
The pop() method is used to remove elements from the end of an array. The pop() method returns the value that was "popped out". It changes the orginal array.

const fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.pop();

6.JavaScript Array push()
The push() method is used to add an element at the end of an Array. As arrays in JavaScript are mutable objects, we can easily add or remove elements from the Array. It changes the orginal array.

let a = [10, 20, 30, 40, 50];
a.push(60);
a.push(70, 80, 90);
console.log(a);

Shifting Elements

Shifting is equivalent to popping, but working on the first element instead of the last.

7.JavaScript Array shift()
The shift() method removes the first array element and "shifts" all other elements to a lower index. It used to remove elements from the beginning of an array. The shift() method returns the value that was "shifted out".

const fruits = ["Banana", "Orange", "Apple", "Mango"];
let fruit = fruits.shift(); //[Orange, Apple, Mango]

8.JavaScript Array unshift()
The unshift() method adds a new element to an array (at the beginning), and "unshifts" older elements. The unshift() method returns the new array length. It used to add elements to the front of an Array.

const fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.unshift("Lemon");

9.JavaScript Array delete Operator
The delete operator is used to delete the given value which can be an object, array, or anything. Using delete() leaves undefined holes in the array.

const fruits = ["Banana", "Orange", "Apple", "Mango"];
delete fruits[0];

To delete object

let emp = { 
    firstName: "Riya", 
    lastName: "Kaur", 
    salary: 40000
} 

console.log(delete emp.salary); 
console.log(emp);

10.JavaScript Array concat() Method
The concat() method is used to concatenate two or more arrays and it gives the merged array. The concat() method creates a new array by merging (concatenating) existing arrays. The concat() method does not change the existing arrays. It always returns a new array. The concat() method can take any number of array arguments. The concat() method can also take strings as arguments:

const arr1 = ["Cecilie", "Lone"];
const arr2 = ["Emil", "Tobias", "Linus"];
const arr3 = ["Robin", "Morgan"];
const myChildren = arr1.concat(arr2, arr3);

11.JavaScript Array copyWithin()
The copyWithin() method copies array elements to another position in an array. The copyWithin() method overwrites the existing values. The copyWithin() method does not add items to the array. The copyWithin() method does not change the length of the array.

const fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.copyWithin(2, 0);

12.JavaScript Array flat()
The flat() method creates a new array with sub-array elements concatenated to a specified depth. The flat() method is used to flatten the array i.e. it merges all the given array and reduces all the nesting present in it.

const myArr = [[1,2],[3,4],[5,6]];
const newArr = myArr.flat();

13.JavaScript Array splice()
The splice() method can be used to add new items to an array. The splice() method returns an array with the deleted items.

const fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.splice(2, 0, "Lemon", "Kiwi");

The first parameter (2) defines the position where new elements should be added (spliced in).
The second parameter (0) defines how many elements should be removed.
The rest of the parameters ("Lemon" , "Kiwi") define the new elements to be added.

14.JavaScript Array slice()
The slice() method slices out a piece of an array into a new array. The slice() method creates a new array. The slice() method does not remove any elements from the source array.

const a = [1, 2, 3, 4, 5];
const res = a.slice(1, 4);
console.log(res); 
console.log(a)

The slice() method creates a new array by extracting elements from index 1 to 3 (exclusive of 4) from the original array. The original array remains unchanged, and the result is [2, 3, 4].

15.Array.map()
Transforms every element of an array and returns a new array without mutating the original. It creates an array by calling a specific function on each element present in the parent array.

const numbers = [1, 2, 3, 4];
const squares = numbers.map(n => n ** 2);
console.log(squares); // [1, 4, 9, 16]

16.Array.filter()
Returns a new array containing only the elements that match a certain condition. It creates a new array with all elements that pass the test implemented by the provided function.

const words = ['apple', 'banana', 'kiwi', 'pear'];
const longWords = words.filter(word => word.length > 4);
console.log(longWords); // ['apple', 'banana']

Object in JavaScript

Raghul — Mon, 13 Jul 2026 17:05:29 +0000

Object in JavaScript

An object is a dynamic data structure that stores related data as key-value pairs, where each key uniquely identifies its value. The values of properties can be primitives, objects, or functions (known as methods when defined inside an object). Objects are mutable and dynamic properties can be added, modified, or deleted at any time. Objects allow data grouping and encapsulation, making it easier to manage related information and behaviour together.

How to Create an Object in JavaScript

1.Using Object Literal Syntax
This is the most popular way to create an object in JavaScript. In this way, we create a JavaScript object by enclosing it within curly braces {}.

let laptop = {
  brand: "Apple",
  model: "MacBook Air",
  operatingSystem: "MacOS"
};

The above code snippet creates a JavaScript object named laptop using curly braces. Within the curly braces, three properties are mentioned, separated by commas.

2.Using Object Constructor Function
This way uses the Object constructor along with the new keyword.

let laptop = new Object(); // This creates an empty object

// Now we will add properties to the object
laptop.brand = "Alienware";
laptop.model = "m15";
laptop.operatingSystem = "Windows 11 Home";

console.log(laptop);
//→ {brand: "Alienware", model: "m15", operatingSystem: "Windows 11 Home"}

The above code creates an empty object using new Object(). Then, we add three properties to this empty object. The resultant object is identical to the one created using the object literal syntax.

3.Using the Object.create Method
This method is used when we wish to inherit properties from an existing object while creating a new object.

let animal = {
  diet: null,
  saySomething: function(word) { console.log(word); }
};

let cat = Object.create(animal);

console.log(cat.diet);
//→ null

cat.saySomething("Meeow");
//→ Meeow

In the above code snippet, the object cat inherits the properties diet and saySomething() from the object animal while the former object is being created. The object animal acts as the parent object, and cat is the child object. Changing the child property diet’s value does not affect the corresponding property for the parent object.

4.Using Object.assign Method
This method is used when we wish to include properties from multiple other objects into the new object we are creating.

let lesson = {
  lessonName: "Data Structures"
};

let teacher = {
  teacherName: "Himmat Singh"
};

let course = Object.assign({}, lesson, teacher);

console.log(course);
//→ {lessonName: "Data Structures", teacherName: "Himmat Singh"}

In the above example, we create a new object named course and include all properties from two objects — lesson and teacher — into it. The properties from the source objects get copied to the target object {}, resulting in the object variable course.

Functions in JavaScript

Raghul — Thu, 09 Jul 2026 16:27:27 +0000

Functions in JavaScript

Functions are one of the fundamental building blocks designed to perform specific tasks in JavaScript. They allow you to organize, reuse, and modularize code. They can take inputs, perform actions, and return outputs. In functions, parameters are placeholders defined in the function, while arguments are the actual values you pass when calling the function.
Uses of function
1.Code reusability
2.Modularity
3.Readability
4.Maintainaability

function greet(name) {   // 'name' is a parameter
  console.log("Hello " + name);
}

greet("Alice");  // "Alice" is the argument

Return Statement
The return statement is used to send a result back from a function. When return executes, the function stops running at that point. The returned value can be stored in a variable or used directly.

function add(a, b) {
  return a + b; // returns the sum
}

let result = add(5, 10);
console.log(result);

Type of Function
Here are the three main types of functions in JavaScript:

1. Named Function
A function that has its own name when declared. It’s easy to reuse and debug because the name shows up in error messages or stack traces.

function greet() {
  return "Hello!";
}
console.log(greet());

2. Function Expression
A function expression is a function created as part of an expression and assigned to a variable or passed to another function. It can be named or anonymous.

const add = function(a, b) {
  return a + b;
};
console.log(add(2, 3));

3. Arrow Function
A new way to write functions using the => syntax. They are shorter and do not have their own this binding, which makes them useful in some cases.

const square = n => n * n;
console.log(square(4));

4. Constructor Function
A special type of function used to create multiple objects with the same structure. It’s called with the new keyword.

function Person(name, age) {
  this.name = name;
  this.age = age;
}

const user = new Person("Neha", 22);
console.log(user.name);

5. Nested Functions
Functions defined within other functions are called nested functions. They have access to the variables of their parent function.

function outerFun(a) {
    function innerFun(b) {
        return a + b;
    }
    return innerFun;
}

const addTen = outerFun(10);
console.log(addTen(5));

Loops concept in JavaScript

Raghul — Wed, 08 Jul 2026 14:42:10 +0000

JavaScript Loops

Loops in JavaScript allow a block of code to run multiple times as long as a given condition is satisfied. They help reduce repetition and make programs more efficient and organized. Loops offer a quick and easy way to do something repeatedly. Loops can execute a block of code a number of times. Loops continue running until the condition becomes false.

*In JavaScript, there are three types of Loops : *

1. for Loop
A for loop repeats until a specified condition evaluates to false. The for loop repeats a block of code a specific number of times. It contains initialization, condition, and increment/decrement in one line. The for statement creates a loop with 3 optional expressions:

for (expr1; expr2; expr3) {
  // code block to be executed
}

exp1 is executed one time before the execution of the code block.
exp2 defines the condition for executing the code block.
exp3 is executed every time the code block has been executed.

2. while Loop
The while loop executes as long as the condition is true. It can be thought of as a repeating if statement. The while loop loops through a block of code as long as a specified condition is true.

let i = 0;
while (i < 3) {
    console.log("Number:", i);
    i++;
}

3. do-while Loop
The do-while loop is similar to while loop except it executes the code block at least once before checking the condition. The do while loop is a variant of the while loop. This loop will execute the code block once, before checking if the condition is true, then it will repeat the loop as long as the condition is true.

let i = 0;
do {
    console.log("Iteration:", i);
    i++;
} while (i < 3);

The do while runs at least once, even if the condition is false from the start.
This is because the code block is executed before the condition is tested.

Loop concept in JavaScript

Raghul — Wed, 08 Jul 2026 14:41:13 +0000

JavaScript Loops

*In JavaScript, there are three types of Loops : *

for (expr1; expr2; expr3) {
  // code block to be executed
}

exp1 is executed one time before the execution of the code block.
exp2 defines the condition for executing the code block.
exp3 is executed every time the code block has been executed.

let i = 0;
while (i < 3) {
    console.log("Number:", i);
    i++;
}

let i = 0;
do {
    console.log("Iteration:", i);
    i++;
} while (i < 3);

The do while runs at least once, even if the condition is false from the start.
This is because the code block is executed before the condition is tested.

if Conditions in JavaScript

Raghul — Mon, 06 Jul 2026 15:46:47 +0000

JavaScript - Conditional Statements

JavaScript conditional statements are used to make decisions in a program based on given conditions. They control the flow of execution by running different code blocks depending on whether a condition is true or false. Conditions are evaluated using comparison and logical operators.

***Reasons to Use Conditional *

Control Program Flow: Decide which code to execute based on different situations.
Make Decisions: React differently to user input, data values, or system states.
Enhance Interactivity: Enable dynamic behavior in apps and websites.
Handle Multiple Scenarios: Manage different outcomes or error handling paths.
Improve Code Flexibility: Write adaptable, reusable code that can respond to change.

Types of Conditional Statements

1. if Statement
The if statement checks a condition written inside parentheses. If the condition evaluates to true, the code inside {} is executed; otherwise, it is skipped.

let x = 20;

if (x % 2 === 0) {
    console.log("Even");
}

if (x % 2 !== 0) {
    console.log("Odd");
};
// output: Even

2. if-else Statement
The if-else statement executes one block of code if a condition is true and another block if it is false. It ensures that exactly one of the two code blocks runs. Used when there are two possible outcomes. The else block runs when the if condition is not satisfied.

let age = 25;

if (age >= 18) {
    console.log("Adult")
} else {
    console.log("Not an Adult")
};
//output: Adult

3. else if Statement
The else if statement is used to test multiple conditions in sequence. It executes the first block whose condition evaluates to true. Allows checking more than two conditions. Evaluated from top to bottom until a true condition is found.

const x = 0;

if (x > 0) {
    console.log("Positive.");
} else if (x < 0) {
    console.log("Negative.");
} else {
    console.log("Zero.");
};
//output: Zero

4. Using Switch Statement (JavaScript Switch Case)
The switch statement evaluates an expression and executes the matching case block based on its value. It provides a clean and readable way to handle multiple conditions for a single variable. Used when one variable needs to be compared against multiple fixed values. Improves readability compared to long if...else if chains.

const marks = 85;

let Branch;

switch (true) {
    case marks >= 90:
        Branch = "Computer science engineering";
        break;
    case marks >= 80:
        Branch = "Mechanical engineering";
        break;
    case marks >= 70:
        Branch = "Chemical engineering";
        break;
    case marks >= 60:
        Branch = "Electronics and communication";
        break;
    case marks >= 50:
        Branch = "Civil engineering";
        break;
    default:
        Branch = "Bio technology";
        break;
}

console.log(`Student Branch name is : ${Branch}`);

//output: Student Branch name is : Mechanical engineering

5. Using Ternary Operator ( ?: )
The ternary operator is a compact shorthand for an if...else statement. It is called “ternary” because it takes three operands:

A condition to test.
An expression to evaluate if the condition is true.
An expression to evaluate if the condition is false.

condition ? expressionIfTrue : expressionIfFalse

let age = 21;

const result =
    (age >= 18) ? "You are eligible to vote."
        : "You are not eligible to vote.";

console.log(result);
//output: You are eligible to vote.

6. Nested if...else[TBD]
A nested if...else statement is an if...else block written inside another if or else. It is used to evaluate multiple related conditions in a hierarchical manner. Useful for handling complex decision-making logic. Deep nesting should be avoided to maintain code readability.

let weather = "sunny";
let temp = 25;

if (weather === "sunny") {
    if (temp > 30) {
        console.log("It's a hot day!");
    } else if (temp > 20) {
        console.log("It's a warm day.");
    } else {
        console.log("It's a bit cool today.");
    }
} else if (weather === "rainy") {
    console.log("Don't forget your umbrella!");
} else {
    console.log("Check the weather forecast!");
};
//output: It's a warm day.