JavaScript Data Types: A Complete Guide

In JavaScript, data types are fundamental building blocks that define the type of data a variable can hold. Understanding data types is essential for writing reliable and bug-free code. This tutorial will cover all the key data types in JavaScript, how they behave, and how to use them effectively.

1. Primitive Data Types

JavaScript has seven primitive data types. These are immutable and represent a single value.

🔹 1.1 String

Represents a sequence of characters.

let name = "John";

🔹 1.2 Number

Represents both integers and floating-point numbers.

let age = 25;
let price = 99.99;

🔹 1.3 Boolean

Represents either true or false.

let isLoggedIn = true;

🔹 1.4 Undefined

A variable that has been declared but not assigned a value.

let score;
console.log(score); // undefined

🔹 1.5 Null

Represents an explicitly empty or non-existent value.

let data = null;

🔹 1.6 Symbol (ES6)

Represents a unique and immutable value.

let id = Symbol("id");

🔹 1.7 BigInt (ES11)

Used to represent integers with arbitrary precision.

let bigNumber = 1234567890123456789012345678901234567890n;

2. Non-Primitive (Reference) Data Types

These are more complex data types and are mutable.

🔸 2.1 Object

Used to store collections of data.

let person = {
  name: "Alice",
  age: 30
};

🔸 2.2 Array

A special type of object used to store ordered collections.

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

🔸 2.3 Function

Functions are objects that can be executed.

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

3. Type Checking

You can check the type of a variable using the typeof operator:

typeof "hello"; // "string"
typeof 42;       // "number"
typeof true;     // "boolean"
typeof null;     // "object" (this is a quirk in JavaScript)
typeof undefined;// "undefined"
typeof [];       // "object"
typeof {};       // "object"
typeof function() {}; // "function"

4. Dynamic Typing

JavaScript is dynamically typed, which means variables can hold values of any type and can be reassigned:

let data = "Hello";
data = 42; // valid

5. Type Conversion

JavaScript automatically converts data types in some cases (type coercion), and you can also convert manually:

🔸 Implicit Conversion:

let result = "5" + 1; // "51"

🔸 Explicit Conversion:

Number("5");   // 5
String(123);   // "123"
Boolean(0);    // false

Final Thoughts

Understanding JavaScript data types is essential for mastering the language. Whether you're working with simple strings and numbers or complex objects and functions, knowing how data types behave will help you write clean, efficient, and bug-free code.

Keep practicing, and explore how different types interact with each other as you build more complex applications!