SOLID / DRY principles

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In software development, Object-Oriented Design plays a crucial role when it comes to writing flexible, scalable, maintainable, and reusable code. There are so many benefits of using OOD but every developer should also have the knowledge of the SOLID principle for good object-oriented design in programming. The SOLID principles are designed to help developers design robust, maintainable applications. The five SOLID principles are: Single-responsibility principle - Function and classes should have one job. Open–closed principle - Classes and functions should be open for  extension but not for modification. Liskov substitution principle - Child class can replace parent class Interface segregation principle - This principle is the first principle that applies to Interfaces instead of classes in SOLID and it is similar to the single responsibility principle. It states that “do not force any client to implement an interface which is irrelevant to them“. Here your main goal is ...
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Hoisting in Javascript

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"Java script putting function declarations into memory before it executes any code segment is that it allows you to use a function before you declare it in your code

Hoisting is a JavaScript mechanism where variables and function declarations are moved to the top of their scope before code execution.This means that no matter where functions and variables are declared, they are moved to the top of their scope regardless of whether their scope is global or local


Note : JavaScript only hoists declarations, not initialization. If a variable is declared and initialized after using it, the value will be undefined.


Ex : 

num = 100; // Initialization

console.log(name) // 100

var  num; // Declaration 



console.log(name) // Undefined

var  num = 100; // Declaration 

Here only declaration will go on the top not initialization.


let Vs var

The main difference between let and var is that scope of a variable defined with let is limited to the block in which it is declared while variable declared with var has the global scope.


In the Javascript engine there are different types of space, when we creates variable using var keyword then that variable will be available in global space and crating variable using let keyword that variable will be not available in global space. 


Why let variables is not Hoistable

            Using let and const keyword, creating variables then that variable will available in temporal dead zone and all the temporal dead zone variable and functions will be not hoistable.

              

Ex : 

1. Using Let

num = 100; //Initialization

let num; // Declaration -- // Throws Reference-error: Cannot access 'num' before initialization

2. Using Const

num = 100; //Initialization

const num; // Declaration --// Throws SyntaxError: Missing initializer in const declaration


Note: Creating variables in java script using let and const that variable will be not hoistable.

above example will valid for functions as well.


let Vs Const

Cannot update const variable. const variable means it is immutable but in case of object we can update property value of object.the properties of a const variable can change. That's because the entire object is not immutable. It just can't be reassigned entirely.

Ex : In case of Variable

const name = "Manohar";

name = "Manu";

Above example will through error

Ex: 

const person = { name: 'Manohar', age: 25}person.age = 27

Above example will not throw any error, here we are changing only property not object.


Creating Variable using let keyword then we can re-initialize that variables.

Ex : 

let name = "Manohar";

name = "Manu";

console.log(name) //Manu 











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