JavaScriptBasics

JavaScript Data Types

Learn JavaScript data types, including primitive and non-primitive types, understand how data is stored, and see real-world examples used in modern JavaScript applications.

What are Data Types in JavaScript?Link to this section

Data types define the type of data a variable can hold. JavaScript is a dynamically typed language, which means you do not need to explicitly specify the data type of a variable—the JavaScript engine determines it automatically at runtime. Understanding data types is essential because different operations behave differently depending on the type of data being used.

Categories of JavaScript Data TypesngLink to this section

JavaScript data types are broadly divided into two categories:
  • Primitive Data Types
  • Non-Primitive (Reference) Data Types

Primitive Data TypesLink to this section

Primitive data types store single, simple values and are immutable.

Number

The Number type is used to store both integers and floating-point values.

note

JavaScript does not have separate types for integers and decimals—both are treated as Number.

String

The String type represents text and is enclosed within single quotes, double quotes, or backticks.

tip

Use meaningful strings to improve readability and user experience in applications.

Boolean

Boolean represents logical values and can have only two values: true or false.

Undefined

A variable that is declared but not assigned a value has the value undefined.

note

Undefined usually indicates that a variable exists but has not been initialized yet.

Null

Null represents the intentional absence of a value.

tip

Use null when you want to explicitly clear or reset a variable’s value.

Symbol

Symbol is a unique and immutable data type introduced in ES6, often used for unique identifiers.

BigInt

BigInt is used to store very large integers that exceed the Number limit.

warning

BigInt cannot be mixed directly with Number values in calculations.

Non-Primitive (Reference) Data TypesLink to this section

Non-primitive data types can store collections of values and are mutable.

Object

Objects store data in key-value pairs.

Array

Arrays are used to store multiple values in a single variable.

Function

Functions are reusable blocks of code and are also treated as data types in JavaScript.

Checking Data Types Using typeofLink to this section

JavaScript provides the typeof operator to check the data type of a variable.

warning

<b>typeof null </b>returns <b> "object", </b>which is a known JavaScript quirk.

Why Understanding Data Types is ImportantLink to this section

  • Prevents runtime errors
  • Helps write efficient logic
  • Improves debugging skills
  • Essential for APIs and database handling

    • tip

    Strong understanding of data types makes learning advanced JavaScript much easier.
    Check Your Understanding
    Question 1 of 5

    JavaScript is a dynamically typed language.

    Identify the Type

    easy

    Declare variables of type Number, String, Boolean, and Null, then identify their types using typeof....

    Fix the Bug

    easy

    Why does the following code behave unexpectedly?...

    typeof null;

    Create an Object

    medium

    Create an object to store details of a course including title, duration, and price....

    Array Practice

    medium

    Create an array of your favorite programming languages and access the second element....