Do you know about Let,Const and Var on javascript?

 let, const, and var are three keywords for declaring variables in Javascript.

1. let

Scope: 

Block-scoped. 

• A variable declared with let is only accessible within the block (code enclosed in curly braces {}) where it's declared.
•  This is crucial for preventing accidental variable reassignment from outer scopes.

Reassignment: 

• Allowed. You can change the value stored in a let variable after it's declared.

Temporal Dead Zone (TDZ): 

• Variables declared with let exist in a TDZ before their declaration, meaning you cannot access or modify them until they are fully declared. 

This is in contrast to var and const hoisting behavior.

Example:

if (true) {

  let foo = 10; // Accessible only within this block

  console.log(foo); // Output: 10

}

console.log(foo); // ReferenceError: foo is not defined (TDZ)

2. const:

Scope: 

• Block-scoped, similar to let.

Reassignment: 

• Not allowed. Once you assign a value to a const variable, you cannot modify it later. 
• This helps prevent unintended changes and potential bugs.

Hoisting: 

• Not hoisted. const declarations are not moved to the top of their scope like var declarations. They must be declared before use.

Example:

const foo = 111;  // Declaring a constant value

foo = 333; // TypeError: Assignment to constant variable

3. var:

Scope: Function-scoped. 

• A variable declared with var is accessible throughout the function where it's declared, even within nested blocks. 
• This can be problematic for large codebases as it can lead to unintended side effects and variable naming conflicts.

Reassignment: 

• Allowed, like let.

Hoisting: 

• Hoisted. var declarations are moved to the top of their scope (function or global scope) during compilation, making them accessible before their declaration. 
• This can be confusing and lead to unexpected behavior if not used carefully.

Example:

for (var i = 0; i < 3; i++) {
  console.log(i); // Output: 0, 1, 2
}

console.log(i); // Output: 3 (accessible even outside the loop due to hoisting)

Best Practices:

• In modern JavaScript development, it's strongly recommended to use const and let instead of var due to their improved scoping behavior and reduced risk of unintended variable reassignment.
• Prefer const for variables that should remain constant throughout the code, and use let when you need to reassign values. 

Note:

const id=6767676

let name='abcd'

var pwd="886876"

city="Bangalore"

1.id=10 //not allowed

2.name="bgbg"

3.pwd="78787"

4.city="hyd"

Prefer not to use var because there was an issue with the block-scoped and functional scope, we use let instead of var.