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Home Interviews var, let, and const in JavaScript. – MindStick
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1 Answers

Amrith Chandran
Amrith Chandran 04 Nov 2025
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Let's understand the differences between var, let, and const in JavaScript with the help of simple examples.

var

  • Declared variables have function scope (not block scope).
  • They can be redeclared and updated.
  • Supports hoisting (moved to the top of the scope, initialized with undefined).

Example-

var name = "Manish";
console.log(name); // output- Manish

var name = "Sharma"; // Redeclare the name variable with new value
console.log(name); // output- Sharma

if (true) {
 var age = 30; // var ignores block level scope
}
console.log(age); // 30 (accessible outside block)

let

  • Declared variables are block-scoped (only within the {}).
  • They can be updated, but not redeclared in the same scope.
  • They are not hoisted in the same way (they exist in a "temporal dead zone" until defined).

Example-

let city = "Delhi";
console.log(city); //output- Delhi
city = "Mumbai"; // can update or reasign a new value
console.log(city); //output- Mumbai

let city = "Noida"; // Return error: can't redeclared

if (true) {
 let country = "India";
 console.log(country); //output- India
}
// console.log(country); //Return error (not accessible outside block)

const

  • Declared variables are block-scoped (only within the {}).
  • It is mandatory to initialize it when declaring it.
  • It cannot be updated or redeclared.
  • For objects/arrays, you can modify their contents (but not reassign them).

Example-

const pi = 3.1416;
// pi = 3.14; // Error - cannot reassign
const user = { name: "Manish" };

user.name = "Sharma"; // allowed (object content can change)
console.log(user.name); // outout- Sharma

// user = { name: "New" }; // Error - cannot reassign object

Let's see a quick example to compare all.

function demo() {
 var a = 10;
 let b = 20;
 const c = 30;
 if (true) {
   var a = 100; // same variable (function-scoped)
   let b = 200; // new variable (block-scoped)
   const c = 300; // new variable (block-scoped)
   console.log(a, b, c); // output- 100 200 300
 }
 console.log(a, b, c); // output- 100 20 30
}
demo();

Would you like to learn about: What is a Service Worker, and how does it differ from a traditional JavaScript script?

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