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Data Types in JavaScript

Introduction

Data Types specify the type of value that a variable can hold.

JavaScript is a Dynamically Typed Language, which means the data type of a variable is determined automatically at runtime based on the value assigned to it.

Example:

let name = "Basha";   // String
let age = 25;         // Number
let status = true;    // Boolean

Types of Data Types in JavaScript

JavaScript Data Types are classified into two categories:

  1. Primitive Data Types
  2. Non-Primitive Data Types

1. Primitive Data Types

Primitive data types are simple data types that store a single value.

The Primitive Data Types are:

  • String
  • Number
  • Boolean
  • Undefined
  • Null

a. String Data Type

A String is a sequence of characters enclosed within:

  • Double Quotes " "
  • Single Quotes ' '
  • Backticks ` `

Example

var firstName = "John";

console.log(firstName);
console.log(typeof(firstName));

var middleName = 'Doe';

console.log(middleName);
console.log(typeof(middleName));

Output

John
string

Doe
string

b. Number Data Type

The Number data type stores:

  • Integer values
  • Floating-point values

Example

var age = 30;

console.log(age);
console.log(typeof(age));

var percentage = 85.5;

console.log(percentage);
console.log(typeof(percentage));

Output

30
number

85.5
number

c. Boolean Data Type

Boolean stores only two values:

  • true
  • false

Example

var isMarried = true;

console.log(isMarried);
console.log(typeof(isMarried));

var pass = false;

console.log(pass);
console.log(typeof(pass));

Output

true
boolean

false
boolean

d. Undefined Data Type

A variable that is declared but not assigned any value is called Undefined.

Example

var myVariable;

console.log(myVariable);
console.log(typeof(myVariable));

var anotherVariable = undefined;

console.log(anotherVariable);
console.log(typeof(anotherVariable));

Output

undefined
undefined

undefined
undefined

e. Null Data Type

Null represents the intentional absence of a value.

Example

var emptyValue = null;

console.log(emptyValue);
console.log(typeof(emptyValue));

var anotherEmptyValue = null;

console.log(anotherEmptyValue);
console.log(typeof(anotherEmptyValue));

Output

null
object

null
object

Important Note:

In JavaScript, typeof null returns "object".

This is a historical bug in JavaScript that has been kept for backward compatibility.

2. Non-Primitive Data Types

Non-Primitive Data Types are complex data structures that can store multiple values.

The Non-Primitive Data Types are:

  • Object
  • Array

a. Object Data Type

An Object is a collection of key-value pairs.

Example

var person = {

    name: "John",
    age: 30,
    isMarried: true

};

console.log(person);

console.log(typeof(person));

Output

{
 name: 'John',
 age: 30,
 isMarried: true
}

object

Another Example

var anotherPerson = {

    name: "Jane",
    age: 25,
    isMarried: false

};

console.log(anotherPerson);

console.log(typeof(anotherPerson));

Output

{
 name: 'Jane',
 age: 25,
 isMarried: false
}

object

b. Array Data Type

An Array is an ordered collection of values.

Arrays can store:

  • Numbers
  • Strings
  • Booleans
  • Objects
  • Mixed Data Types

Example

var numbers = [1, 2, 3, 4, 5];

console.log(numbers);

console.log(typeof(numbers));

Output

[1, 2, 3, 4, 5]

object

Another Example

var fruits = ["apple", "banana", "orange"];

console.log(fruits);

console.log(typeof(fruits));

Output

['apple', 'banana', 'orange']

object

Primitive vs Non-Primitive Data Types

Primitive Non-Primitive
Stores Single Value Stores Multiple Values
Immutable Mutable
Stored by Value Stored by Reference
Faster Access Comparatively Slower
Examples: String, Number, Boolean Examples: Object, Array

Complete List of JavaScript Data Types

Primitive Data Types

  1. String
  2. Number
  3. Boolean
  4. Undefined
  5. Null

Non-Primitive Data Types

  1. Object
  2. Array

Important Notes

  1. JavaScript is a Dynamically Typed Language.
  2. typeof() is used to determine the data type of a variable.
  3. Arrays are special types of Objects.
  4. typeof null returns "object" because of a historical JavaScript bug.
  5. Primitive values are stored by value.
  6. Objects and Arrays are stored by reference.

Summary

JavaScript supports two categories of data types:

  • Primitive Data Types

    • String
    • Number
    • Boolean
    • Undefined
    • Null

  • Non-Primitive Data Types

    • Object
    • Array

Understanding data types is fundamental for learning variables, operators, functions, objects, arrays, DOM manipulation, and advanced JavaScript concepts.