What is the difference between let, const, and var?

Answer:

1. Scope:

var is function-scoped.
let and const are block-scoped, meaning they are only accessible within the block where they are defined.

2. Redeclaration:

var allows redeclaration of the same variable in the same scope.
let and const do not allow redeclaration in the same scope.

3. Reassignment:

var and let allow reassignment.
const does not allow reassignment after initialization.

4. Hoisting:

var is hoisted and initialized as undefined.
let and const are hoisted but remain uninitialized until their declaration is encountered. Accessing them before declaration results in a ReferenceError.

Examples

var example

function exampleVar() {
  var x = 10;
  if (true) {
    var x = 20; // Same variable, re-declared
    console.log(x); // 20
  }
  console.log(x); // 20
}
exampleVar();

let example

function exampleLet() {
  let x = 10;
  if (true) {
    let x = 20; // Different variable due to block scope
    console.log(x); // 20
  }
  console.log(x); // 10
}
exampleLet();

const example

function exampleConst() {
  const x = 10;
  // x = 20; // Error: Assignment to constant variable
  console.log(x); // 10
}
exampleConst();

Key Points

Use let for variables that will be reassigned later.
Use const for variables that should not change.
Avoid var in modern JavaScript development due to its function-scoping and hoisting behavior.