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JavaScript Data Types

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JavaScript Data Types

JavaScript data types describe the kind of value you can store in a variable. Understanding data types is important because they help you work with numbers, text, true/false values, objects, and more.

JavaScript has two main categories of data types:

  • Primitive Data Types
  • Non-Primitive (Reference) Data Types

Let’s explore them in simple terms.

1. Primitive Data Types

Primitive types are simple and cannot be changed once created (they are immutable). JavaScript has 7 primitive data types.

1.1 Number

Represents numeric values such as integers and decimals.

Example
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let age = 25;
let price = 99.99;
1.2 String

Represents text and characters. You can use single quotes, double quotes, or backticks.

Example
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let name = "learn2kode";
let city = 'Chennai';
let message = `Welcome to Learn2Kode`;
1.3 Boolean

Represents true or false.

Example
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let isLoggedIn = true;
let isPaid = false;
1.4 Undefined

A variable that is declared but not assigned a value.

Example
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let value;
console.log(value); // undefined
1.5 Null

Represents empty or no value. You assign it manually.

Example
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let data = null;
1.6 BigInt

Used for very large numbers beyond JavaScript’s normal limit.

Example
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let bigNumber = 12345678901234567890123456789n;
1.7 Symbol

Used to create unique identifiers, helpful in advanced JavaScript.

Example
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let id = Symbol("userID");

2. Non-Primitive (Reference) Data Types

These are mutable and store collections or complex data.

2.1 Object

An object stores key–value pairs.

Example
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let user = {
  name: "learn2kode",
  age: 25,
  city: "Chennai"
};

2.2 Array

A list of values, stored inside square brackets.

Example
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let colors = ["red", "blue", "green"];

2.3 Function

Functions themselves are considered data types.

Example
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function greet() {
  console.log("Hello!");
}

Summary Table

How to Check Data Type

Use the typeof operator:

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console.log(typeof "Hello"); // string
console.log(typeof 25);      // number
console.log(typeof true);    // boolean
console.log(typeof {});      // object
console.log(typeof []);      // object (arrays are objects)
console.log(typeof null);    // object (JavaScript bug)

Important Notes

Use the typeof operator:

  • null returns "object" → known JavaScript bug
  • Arrays return "object" → because they are special objects
  • Functions return "function" but are still objects internally
JavaScript Variables
JavaScript Operators