let and const

Modern JavaScript provides let and const for declaring variables with block scope.

What are let and const?

In modern JavaScript, let and const are used to declare variables.

Both are block-scoped, but they are different in how their values can be changed.

Simple Definition

let is used when a variable's value may change, while const is used when the variable should not be reassigned.

Difference between let and const in JavaScript

let vs const

Feature	let	const
Block Scoped	Yes	Yes
Reassignment	Allowed	Not Allowed
Redeclaration in Same Scope	No	No
Must Initialize	No	Yes

Example 1: Using let

A let variable can be reassigned after it has been declared.

let age = 20;

age = 21;

console.log("Age:", age);

Age: 21

Example 2: Using const

A const variable must be initialized when it is declared and cannot be reassigned.

const course = "JavaScript";

console.log("Course:", course);

Course: JavaScript

Example 3: Changing a let Variable

let marks = 70;

console.log("Before:", marks);

marks = 85;

console.log("After:", marks);

Before: 70
After: 85

Example 4: Block Scope

Variables declared using let and const are available only inside their block.

{
    let city = "Pune";
    const country = "India";

    console.log("City:", city);
    console.log("Country:", country);
}

City: Pune
Country: India

Example 5: let and const Together

let student = "Amit";
const course = "JavaScript";

student = "Rahul";

console.log("Student:", student);
console.log("Course:", course);

Student: Rahul
Course: JavaScript

Important Note

Use let when you know that the variable value needs to change.

Use const by default when the variable should not be reassigned.

Summary

let and const are modern JavaScript variable declarations. Both are block-scoped. The main difference is that let can be reassigned while const cannot be reassigned.