While learning JavaScript, one of the first concepts I wanted to understand properly was data types.
JavaScript has several data types, but they can be divided into two main categories:
Primitive data types
Non-primitive data types
In this post, I'm focusing only on primitive data types.
What is a Primitive Data Type?
A primitive data type represents a single, simple value.
JavaScript has 7 primitive data types:
- String
- Number
- BigInt
- Boolean
- Undefined
- Null
- Symbol
Let's understand each one.
1. String
A String is used to store text.
let name = "John";
let city = "Chennai";
Strings can use:
"Double quotes"
'Single quotes'
Backticks
Example:
let message = "Hello John";
console.log(message);
Output:
Hello John
Check the type:
console.log(typeof message);
Output:
string
2. Number
The Number type is used for numbers, including integers and decimal values.
let age = 25;
let price = 99.99;
let temperature = -10;
All of these are number.
console.log(typeof age);
Output:
number
JavaScript doesn't have separate int and float types like some other programming languages.
3. BigInt
BigInt is used for very large integers that cannot be safely represented by the normal Number type.
Example:
let bigNumber = 123456789012345678901234567890n;
Notice the n at the end.
console.log(typeof bigNumber);
Output:
bigint
You can think of it as:
Number → normal-sized numbers
BigInt → very large integers
*4. Boolean *
A Boolean can have only two values:
true
false
Example:
`let isLoggedIn = true;
let isAdmin = false;
Booleans are commonly used with conditions.
if (isLoggedIn) {
console.log("Welcome John!");
}
Output:
Welcome John!`
5. Undefined
undefined usually means a variable has been declared but hasn't been given a value.
let username;
console.log(username);
Output:
undefined
Example:
let age;
console.log(typeof age);
Output:
undefined
So a simple way to remember it is:
Declared but no value → undefined
6. Null
null represents an intentional absence of a value.
Example:
let selectedUser = null;
Here, we are intentionally saying that there is currently no selected user.
One interesting JavaScript behavior is:
console.log(typeof null);
Output:
object
This is a well-known historical quirk of JavaScript.
Even though typeof null returns "object", null is considered a primitive value.
7. Symbol
Symbol is used to create unique values.
Example:
let id1 = Symbol("id");
let id2 = Symbol("id");
console.log(id1 === id2);
Output:
false
Even though both symbols have the same description, they are different unique values.
Symbols are mainly useful when unique identifiers are needed.
*Quick Cheat Sheet *
Primitive Type Example
String "John"
Number 25
BigInt 123n
Boolean true
Undefined undefined
Null null
Symbol Symbol("id")
One Important Thing
These 7 types are primitive data types in JavaScript:
String
Number
BigInt
Boolean
Undefined
Null
Symbol
Understanding these basics makes it easier to learn the next JavaScript concepts, such as:
Variables
Operators
Type conversion
Conditions
Functions
Arrays
Objects
I'm learning JavaScript step by step, and understanding the basics properly is helping me build a stronger foundation.
What's the JavaScript data type you found confusing at first?
Top comments (1)
Great breakdown! Clear and concise for beginners. 👏
For me, Number vs BigInt was definitely the one that caused the biggest headaches early on, especially two common gotchas:
typeof NaN === 'number': Finding out that "Not-a-Number" is technically of typenumberin JS always confuses beginners!BigIntJSON serialization:BigIntis amazing for 64-bit database IDs, but nativeJSON.stringify()will throw aTypeError: Do not know how to serialize a BigIntunless you supply a custom replacer.Another fun historical quirk with
typeof null === 'object'is that in the original 1995 JS engine, types were stored with 3-bit tags, and000represented objects whilenullwas pointer0x00!Keep up the great writing! 🚀