JavaScript Data Types

A data type tells JavaScript what kind of value a variable stores.

Common JavaScript Data Types

String

A string stores text inside quotes.

let message = "Welcome to JavaScript";

Number

A number stores a whole number or decimal value.

let price = 499;
let rating = 4.5;

Boolean

A boolean stores either true or false.

let isLoggedIn = true;

Undefined

undefined means a variable has no assigned value.

let username;

console.log(username);

Output:

undefined

Null

null is an intentionally empty value.

let selectedProduct = null;

Checking a Data Type

Use typeof to check the data type of a value.

let age = 25;

console.log(typeof age);

Output:

number

Key Takeaways

• String stores text.
• Number stores whole numbers and decimals.
• Boolean stores true or false.
• undefined and null represent missing or empty values.
• Use typeof to check a value's data type.