JavaScript has eight data types, which are divided into two main groups:
- Primitive Data Types
- Non-Primitive Data Types
Note: NaN is not a data type. It is a special numeric value.
Primitive values are stored directly in memory and are not stored as references to objects.
Numeric Type
- Number
- BigInt
Non-Numeric Type
- String
- Boolean
- Null
- Undefined
- Symbol
The Number data type represents both integers and floating-point values. JavaScript numbers are based on the 64-bit floating-point format (IEEE 754).
let age = 25;
let height = 5.8;
console.log(age); // 25
console.log(height); // 5.8console.log() is used to display output in the console. It is mainly used for debugging and checking values while writing JavaScript code.
let name = "Jagan";
console.log(name); // JaganThe safe limit is the range of whole numbers that the Number data type can represent accurately (without losing precision).
- Maximum safe integer:
Number.MAX_SAFE_INTEGER→ 9,007,199,254,740,991- Minimum safe integer:
Number.MIN_SAFE_INTEGER→ −9,007,199,254,740,991
console.log(Number.MAX_SAFE_INTEGER); // 9,007,199,254,740,991
console.log(Number.MIN_SAFE_INTEGER); // −9,007,199,254,740,991BigInt is used to represent very large whole numbers that are greater than the safe limit of the Number type.
let bigOne = 12345678901234567890n;
let bigTwo = BigInt("12345678901234567890");
console.log(bigOne); // 12345678901234567890
console.log(bigTwo); // 12345678901234567890Note: BigInt cannot contain decimal values.
The String data type is used to store text. Strings can be created using single quotes, double quotes, or template literals.
let firstName = "Jagan"; // Double Quotes
let lastName = 'Ganesh'; // Single Quotes
console.log(firstName); // Jagan
console.log(lastName); // GaneshTemplate literals allow you to embed variables, expressions, and multi-line text inside strings.
let name = "Jagan";
let age = 32;
let message = `My name is ${name} and I am ${age} years old.`;
console.log(message); // My name is Jagan and I am 32 years old.A string is made up of individual characters.
Each character in a string has a position, called an index.
In JavaScript, the index starts from 0.
let name = "Jagan";
console.log(name[0]); // J
console.log(name[1]); // a
console.log(name[2]); // gNote: Spaces and special symbols are also counted as characters in a string.
You can find the number of characters in a string using the .length property.
let city = "Chennai";
console.log(city.length); // 7Bracket notation allows you to access individual characters in a string using their index.
// Access First Character
let name = "John";
console.log(name[0]); // "J"
// Access Last Character
let name = "Mike";
console.log(name[name.length - 1]); // "e"Strings are immutable in JavaScript, which means once a string is created, you cannot change its individual characters directly. If you want a different string, you have to create a new string.
let lastName = "Doe";
// Trying to change a character does NOT work
lastName[0] = "J";
console.log(lastName); // "Doe" (remains unchanged)
// Creating a new string works
lastName = "Joe";
console.log(lastName); // "Joe"Strings can be concatenated using the + operator, compound assignment, or template literals.
Escape sequences are used to represent special characters inside strings.
\' → single quote
\" → double quote
\\ → backslash
\n → new line
\t → tab
\r → carriage return (moves the cursor to the beginning of the line; originally used in typewriters)
\b → backspace
\f → form feed (originally used to advance to the next page in printing; now rarely used and implementation-dependent)
A Boolean data type has only two possible values:
truefalse
let isLoggedIn = true;
let hasAdminAccess = false;
console.log(isLoggedIn); // true
console.log(hasAdminAccess); // falsenull is used to represent no value or an empty value.
It is used when you want to intentionally assign nothing to a variable.
let currentUser = null;
console.log(currentUser); // null
console.log(typeof currentUser); // object (this is a known JavaScript quirk)undefined means a variable has been declared but has not been assigned a value.
let name;
console.log(name); // undefined
console.log(typeof name); // undefinedNull → "Nothing here, I put it intentionally" Think of an empty box you placed on purpose.
Undefined → "I forgot to put something here" Think of a box that exists but you never filled.
Symbol is a unique and immutable primitive data type. Symbols are mainly used as unique identifiers for object properties, ensuring that property keys do not conflict with others.
let id1 = Symbol("id");
let id2 = Symbol("id");
console.log(id1 === id2); // false (each Symbol is unique)Note: Symbols are perfect when you need unique, collision-free identifiers — for object keys, constants, or customizing behavior with well-known symbols.
// Create unique symbols for different roles
const admin = Symbol("role");
const editor = Symbol("role");
let user = {};
user[admin] = "Alice";
user[editor] = "Bob";
console.log(user[admin]); // Alice
console.log(user[editor]); // Bob
console.log(admin === editor); // false (each Symbol is unique)Note: Even though both symbols have the same description "role", they are unique identifiers.
Non-Primitive data types, also known as reference types or object types, are used to store collections of data and more complex entities.
Note: Unlike primitive types (which store the actual value), non-primitive variables store a reference to the location of the object in memory.
All non-primitive values in JavaScript are objects.
- Object
- Date
- RegExp
- Array
- Function
An object is used to store data in the form of key-value pairs.
let user = {
name: "Jagan",
age: 25,
isActive: true,
};
console.log(user.name); // Jagan
console.log(user.age); // 25Note: Objects are mutable, which means their values can be changed.
Array values are stored in an ordered list, and each value has an index number (starting from 0).
let fruits = ["Apple", "Banana", "Orange"];
console.log(fruits[0]); // Apple
console.log(fruits[2]); // Orangeconsole.log(fruits.length); // 3Note: Arrays are mutable, meaning elements can be added, removed, or changed.
A function performs a specific task and runs only when it is called.
const greet = (name) => {
console.log("Hello " + name);
};
greet("Jagan"); // Hello Jaganconst myFunc = (isActive) => {
console.log("Argument: " + isActive);
};const add = (a, b) => {
return a + b;
};
console.log(add(5, 10)); // 15Note: If a function does not explicitly return a value, it automatically returns
undefined.
The Date object is used to work with dates and times in JavaScript. It allows you to create, read, and manipulate dates such as the current date, specific dates, and time values.
let today = new Date();
console.log(today); // current date and timelet now = new Date();
console.log(now.getFullYear()); // Year
console.log(now.getMonth()); // Month (0–11)
console.log(now.getDate()); // Day of the month
console.log(now.getHours()); // Hours
console.log(now.getMinutes()); // MinutesNote: The Date object is mutable, meaning its values can be changed using setter methods like
setFullYear(),setMonth(), etc.
The RegExp (Regular Expression) is used to search, match, and manipulate patterns in strings. It is especially useful for validation, searching, and text replacement.
let pattern = /hello/;
let text = "hello world";
console.log(pattern.test(text)); // true