var

• Can be re-declared and updated within its scope.

var name = "Shubham";

// ✅ Below operations are possible
name = "Amit"; // only updating
var name = "Amit"; // re-declaration and updating

• It is not compulsory to initialize a var variable during declaration.

var name;

let

• Can be updated but not re-declared.

let name = "Shubham";

name = "Amit"; // can be updated

// ❌ Below operation is not possible
let name = "Amit"; // re-declaration and updating

• It is not compulsory to initialize a let variable during declaration.

let name;

const

• Can neither be re-declared nor updated.

const name = "Shubham";

// ❌ Below operations are not possible
name = "Amit"; // only updating
const name = "Amit"; // re-declaration and updating

• Must be initialized during declaration.

// ❌ Only declaration is not possible
const name;

Rules for choosing variable names

1. Only letters, digits, underscore(_) and dollar($) allowed.

2. Must begin with a letter or _ or $. Must not begin with a digit.

3. JavaScript reserved words can't be used as a variable name.

4. Variable names are case sensitive (name, Name and NaMe are different variable names).

Happy reading!