In JavaScript, data types determine the type of value stored in a variable.
JavaScript has both primitive data types (which include String, Number, Boolean, Undefined, Null, Symbol, and BigInt) and non-primitive data types (Object, Array, Function).
Table of Contents
1. Primitive Data Types
1.1. String
A string is a sequence of characters used to represent text. Strings are enclosed in single (‘ ‘), double (” “), or backticks (` `) quotes.
let singleQuote = 'Hello, World!';
let doubleQuote = "JavaScript is fun!";
let templateString = `This is a template literal, and you can include variables like ${singleQuote}`;
console.log(singleQuote); // Output: Hello, World!
console.log(doubleQuote); // Output: JavaScript is fun!
console.log(templateString); // Output: This is a template literal, and you can include variables like Hello, World!
1.2. Number
The Number data type is used to represent both integers and floating-point numbers. JavaScript also supports special numeric values like Infinity and NaN (Not-a-Number).
let integer = 42; let float = 3.14; let negative = -7; let infinityValue = Infinity; let notANumber = NaN; console.log(integer); // Output: 42 console.log(float); // Output: 3.14 console.log(negative); // Output: -7 console.log(infinityValue); // Output: Infinity console.log(notANumber); // Output: NaN
1.3. Boolean
A boolean can only have two values: true or false. Booleans are often used in conditional statements to control the flow of the program.
let isJavaScriptFun = true; let isPythonFun = false; console.log(isJavaScriptFun); // Output: true console.log(isPythonFun); // Output: false
1.4. Undefined
A variable that has been declared but not assigned a value has the value undefined.
let undefinedVar; console.log(undefinedVar); // Output: undefined // Declaring a variable explicitly as undefined let explicitlyUndefined = undefined; console.log(explicitlyUndefined); // Output: undefined
1.5. Null
The null value represents an intentional absence of any object value. It is explicitly set by the programmer to indicate “no value.”
let emptyValue = null; console.log(emptyValue); // Output: null
1.6. Symbol
Symbol is a unique and immutable data type that is often used as unique property keys in objects. Each Symbol is unique.
let sym1 = Symbol('description');
let sym2 = Symbol('description');
console.log(sym1 === sym2); // Output: false
console.log(sym1); // Output: Symbol(description)
console.log(sym2); // Output: Symbol(description)
1.7. BigInt
BigInt is a data type introduced in ES2020 that allows you to represent integers larger than the Number type's limit (2^53 – 1).
let bigIntNumber = 123456789012345678901234567890n; // Notice the 'n' at the end console.log(bigIntNumber); // Output: 123456789012345678901234567890n // Operations with BigInt let bigIntSum = bigIntNumber + 10n; console.log(bigIntSum); // Output: 123456789012345678901234567900n
2. Non-Primitive Data Types
2.1. Object
An Object is a collection of key-value pairs. Objects can store various data types and complex entities.
let person = {
firstName: 'John',
lastName: 'Doe',
age: 30,
isEmployed: true
};
console.log(person.firstName); // Output: John
console.log(person['lastName']); // Output: Doe
// Adding a new property
person.country = 'USA';
console.log(person.country); // Output: USA
2.2. Array
Arrays are special types of objects used to store multiple values in a single variable. Array elements are ordered and indexed starting from 0.
let fruits = ['Apple', 'Banana', 'Cherry'];
console.log(fruits[0]); // Output: Apple
console.log(fruits.length); // Output: 3
// Adding an element to the array
fruits.push('Orange');
console.log(fruits); // Output: ['Apple', 'Banana', 'Cherry', 'Orange']
2.3. Function
A function is an object in JavaScript that performs a task or calculates a value. Functions can be assigned to variables, passed as arguments, and returned from other functions.
// Function declaration
function greet(name) {
return `Hello, ${name}!`;
}
console.log(greet('Alice')); // Output: Hello, Alice!
// Function expression
let add = function(a, b) {
return a + b;
};
console.log(add(5, 3)); // Output: 8
3. Dynamic Typing in JavaScript
In JavaScript, a variable can change its type as new values are assigned to it.
let variable = 'I am a string'; console.log(typeof variable); // Output: string variable = 42; // Now the variable is a number console.log(typeof variable); // Output: number variable = true; // Now the variable is a boolean console.log(typeof variable); // Output: boolean
4. Checking Data Types
JavaScript provides the typeof operator to check the data type of a variable.
console.log(typeof 'Hello'); // Output: string
console.log(typeof 123); // Output: number
console.log(typeof true); // Output: boolean
console.log(typeof undefined); // Output: undefined
console.log(typeof null); // Output: object (this is a quirk in JavaScript)
console.log(typeof Symbol('id')); // Output: symbol
console.log(typeof 123n); // Output: bigint
console.log(typeof {}); // Output: object
console.log(typeof []); // Output: object (arrays are objects in JavaScript)
console.log(typeof function(){}); // Output: function
Summary
Primitive data types include: String, Number, Boolean, Undefined, Null, Symbol, and BigInt.
Non-primitive data types include: Object, Array, and Function.
Use typeof to determine the data type of a variable.
JavaScript is dynamically typed, meaning variables can change types during runtime.
This guide provides a comprehensive overview of JavaScript data types with practical code examples to help you understand how to use them effectively in your programming.