What is the difference between let, var and const

var is the older way of declaring variables. It is function-scoped, meaning it is accessible only within the function it is declared in, or globally if declared outside a function. Variables declared with var can be re-declared and updated.

var x = 15;
x = 25; // Allowed
var x = 35; // Allowed

let is a newer way to declare variables. It is block-scoped, meaning the variable is only accessible within the block {} it is declared in. Variables declared with let can be updated but cannot be re-declared within the same block.

let y = 15;
y = 25; // Allowed
// let y = 35; // Not allowed in the same block

const is used for constants. It is block-scoped and cannot be updated or re-declared. However, if the constant is an object or array, its properties or elements can still be modified.

const z = 15;
// z = 25; // Not allowed
const arr = [1, 2, 3];
arr.push(4); // Allowed, we can modify the array

What is the purpose of using the let keyword in JavaScript?

The let keyword in JavaScript is used to declare a block-scoped variable that can be reassigned within its scope. It replaces the older var keyword, which has function scope and can cause unexpected behavior. Using let enhances code clarity and helps prevent issues like accidental variable hoisting.

In summary:

• Use var for function-scoped variables.
• Use let for block-scoped variables that can be updated.
• Use const for block-scoped variables that cannot be updated.