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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Difference between let, var and const in Javascript

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In JavaScript, `var`, `let`, and `const` are used to declare variables, but they have some differences in terms of scoping, reassignment, and hoisting. Here's a breakdown of their key differences:


1. `var`:

   - Variables declared with `var` have function scope or global scope (if declared outside any function).

   - They can be reassigned and redeclared within the same scope without generating errors.

   - `var` variables are hoisted, meaning they are moved to the top of their scope during the compilation phase, allowing them to be accessed before they are declared.

   - Example:


   function example() {

     var x = 10;

     if (true) {

       var x = 20;

       console.log(x); // Output: 20

     }

     console.log(x); // Output: 20

   }

   example();

  


   In this example, the `x` variable is declared with `var` inside the function. When the `if` block is executed, a new assignment to `x` changes its value within the entire function scope.


2. `let`:

   - Variables declared with `let` have block scope, meaning they are limited to the block in which they are defined (e.g., inside loops or conditionals).

   - They can be reassigned but not redeclared within the same scope.

   - `let` variables are not hoisted, so they cannot be accessed before they are declared.

   - Example:


   function example() {

     let x = 10;

     if (true) {

       let x = 20;

       console.log(x); // Output: 20

     }

     console.log(x); // Output: 10

   }

   example();

   ```


   In this example, the `x` variable is declared with `let`. The `let` keyword allows the `x` variable in the `if` block to have a separate scope from the `x` variable in the outer scope.


3. `const`:

   - Variables declared with `const` also have block scope.

   - They must be assigned a value when declared and cannot be reassigned or redeclared within the same scope.

   - `const` variables are not hoisted and follow the same scoping rules as `let` variables.

   - `const` is used for values that are intended to be constant and not changed throughout the program.

   - Example:


   function example() {

     const x = 10;

     if (true) {

       const x = 20;

       console.log(x); // Output: 20

     }

     console.log(x); // Output: 10

   }

   example();

In this example, the `x` variable is declared with `const`. It cannot be reassigned or redeclared within the same scope, preserving its initial value.

It is generally recommended to use `let` or `const` over `var` as they provide block scoping and stricter reassignment rules, which help avoid unintended side effects and make code more maintainable. Use `let` when you need to reassign a variable and use `const` for variables that should not be changed.

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