JavaScript Data Types

🎯 JavaScript Data Types

JavaScript has different data types to store different kinds of information. Variables can hold numbers, text, true/false values, and more.


// Different data types
let name = "John";        // String
let age = 25;             // Number
let isStudent = true;     // Boolean
let hobbies = ["reading", "coding"]; // Array

console.log(typeof name, typeof age, typeof isStudent);

Output:

string number boolean

Primitive Data Types

🔤

String

Text data enclosed in quotes

let text = "Hello World";
let name = 'John';

🔢

Number

Integers and floating-point numbers

let age = 25;
let price = 99.99;

✅

Boolean

True or false values

let isActive = true;
let isComplete = false;

❌

Undefined

Variable declared but not assigned

let x;
console.log(x); // undefined

🔹 String Data Type

Strings represent text data and can be created using single or double quotes:

// Different ways to create strings
let firstName = "John";
let lastName = 'Doe';
let message = `Hello, ${firstName}!`; // Template literal

// String properties and methods
console.log(firstName.length);        // Length of string
console.log(firstName.toUpperCase()); // Convert to uppercase
console.log(message);                 // Template literal result

Output:

4
JOHN
Hello, John!

🔹 Number Data Type

JavaScript has only one number type that can represent both integers and decimals:

// Different types of numbers
let integer = 42;
let decimal = 3.14159;
let negative = -10;
let scientific = 2e3; // 2000

// Special number values
let infinity = Infinity;
let notANumber = NaN;

console.log(integer, decimal, negative, scientific);
console.log(typeof integer); // All are "number" type

Output:

42 3.14159 -10 2000
number

🔹 Boolean and Other Types

Boolean represents true/false values, and there are other special types:

// Boolean values
let isTrue = true;
let isFalse = false;

// Other special types
let nothing = null;        // Intentionally empty
let notDefined;           // undefined
let bigNumber = 123n;     // BigInt for large numbers

// Check types using typeof
console.log(typeof isTrue);    // boolean
console.log(typeof nothing);   // object (special case)
console.log(typeof notDefined); // undefined
console.log(typeof bigNumber);  // bigint

Output:

boolean
object
undefined
bigint

🔹 Complex Data Types

JavaScript also has complex data types for storing collections of data:

// Array - ordered list of values
let colors = ["red", "green", "blue"];
let numbers = [1, 2, 3, 4, 5];

// Object - collection of key-value pairs
let person = {
  name: "John",
  age: 30,
  city: "New York"
};

console.log(colors[0]);        // First array element
console.log(person.name);      // Object property
console.log(typeof colors);    // object
console.log(typeof person);    // object

Output:

red
John
object
object