Data Types & Variables

JavaScript datatypes and variables

• What is Variable?
• Understanding data types
• Declaring and Initialization variables

What is Variable?

variablessss !!

A container which stores some data(value) is known as Variable.

• Where we can store some value.

Understanding data types

A data type determines the kind of value a variable can hold.

JavaScript, being a dynamically-typed language, allows variables to store values of any type, which can even change during runtime.

Types of Datatypes

1. Primitives Data Type
2. Non-Primitive (Reference) Data Types

* Primitives Data Types

These represent single values and are immutable.

a. Number

• Represents numeric values (both integers and floating-point numbers).

let age = 25;       // Integer
let price = 19.99;  // Floating-point
let infinity = Infinity; // Special numeric value

b. String

• Represents text values, enclosed in single ('), double ("), or template literals (```).

let name = "John Doe";        // Double quotes
let greeting = 'Hello!';      // Single quotes
let template = `Hi ${name}`;  // Template literal

c. Boolean

• Represents true or false.

let isJavaScriptFun = true;

d. Undefined

• Represents a variable that has been declared but not assigned a value.

let x; // Undefined
console.log(x); // Outputs: undefined

e. Null

• Represents an intentional absence of any value (empty value).

let y = null;

* Non-Primitive (Reference) Data Types

These are objects and mutable.

a. Object

• Represents a collection of key-value pairs.

let person = {
  name: "Alice",
  age: 30
};

b. Array

• A special type of object used to store ordered collections of values.

let fruits = ["apple", "banana", "cherry"];

c. Function

• A callable object that performs a specific task.

function greet() {
  console.log("Hello!");
}

d. Date

• Represents date and time.

let today = new Date();

Different between Var and Let

var and let both are used to declare variables in JavaScript, but they have some important differences.

• Scope Difference

**var → Function Scoped**

if (true) {
   var name = "Jay";
}

console.log(name); // ✅ works

var ignores block {} scope.

**let → Block Scoped**

if (true) {
   let name = "Jay";
}

console.log(name); // ❌ Error

let only works inside the block where it is created.

• Re-declaration

var

var age = 20;
var age = 30; // ✅ allowed

let

let age = 20;
let age = 30; // ❌ Error

let cannot be re-declared in same scope.

• Update Value Both can update values.

var city = "Surat";
city = "Rajkot"; // ✅

let country = "India";
country = "USA"; // ✅

• Hoisting Both are hoisted, but behavior is different.

var

console.log(a); // undefined

var a = 10;

let

console.log(a); // ❌ Error

let a = 10;