SEJAL YADAV sejalkailashyadav

🌐 What is DNS?

DNS = Domain Name System

It's like the phonebook of the internet.

📱 Real-Life Example

complete one-by-one command flow** for starting MySQL and Apache, then creating and running a PHP file step-by-step:

✅ STEP 1: Start MySQL

sudo systemctl start mysql

🧠 Is dynamic memory (using `new` and `delete`) necessary in C++?

✅ Short Answer:

No, it’s not always necessary.

🔍 When You DON'T Need Dynamic Memory:

very common problem with large forms:

❌ When you submit a big form and Laravel validation fails, it refreshes the page and shows errors… 😩 But the user has to fill everything again or scroll a lot, which is frustrating.

✅ SOLUTION (Best Practice): Use `old()` values + show validation errors properly

You do NOT need to re-enter the entire form if you use Laravel’s built-in helpers the right way.

🔹 Core Concepts of OOP in JavaScript:

Encapsulation: Bundling data (properties) and methods (functions) that work on the data into a single unit, usually a class. It hides the internal details of the object and only exposes what’s necessary.
Abstraction: Hiding complex implementation details and showing only the necessary features to the user.
Inheritance: The mechanism by which one class can inherit properties and methods from another class, allowing for code reuse and a hierarchical class structure.

Asynchronous Programming: Callbacks, Promises, and Async/Await

🔹 What is Synchronous in JavaScript?

Synchronous ka matlab hota hai — ek ke baad ek kaam hona.[sky- one by one]

Jaise ki:

Jab tak pehla kaam pura nahi hota, tab tak dusra start nahi hota.

Immutable Deep Update using Nested Maps:

🔁 Immutable Deep Update using Nested Maps

When working with nested data structures like arrays of objects (e.g., departments with employees), it's important to update values immutably — without modifying the original data.
This pattern uses nested .map() functions to update specific fields deep within the structure.

real-world data to show the difference between using map().flat() and flatMap().

Scenario: A List of Orders and Items

You have an array of orders, and each order contains an array of items. You want to flatten the items from all orders into a single list.

1. Using `map()` and `flat()`

Disable a Link Using Only CSS

Overview

This guide explains how to disable an anchor (<a>) link using only CSS, without JavaScript.

Example

We use the pointer-events: none; and color: gray; properties to visually and functionally disable the link.

	### ✅ You can use `map()` on:

	1. An array of values
	2. An array of objects
	3. An array of arrays
	Basically, any array.

	---

	### 🔹 1. Array of values