JavaScript Data Types

JavaScript is a dynamically typed language, meaning variables can hold any type of data, and types are determined at runtime. Data types fall into two categories: primitive types and reference types.

🔢 1. Primitive Data Types

• String – Represents text: "Hello", 'World'
• Number – Both integers and floating-point: 42, 3.14
• Boolean – True or false: true, false
• Undefined – A declared variable with no value
• Null – An intentional absence of any object value
• BigInt – For very large integers: 12345678901234567890n
• Symbol – Unique and immutable value often used as object keys

let name = "Alice";     // String
let age = 30;           // Number
let isAdmin = true;     // Boolean
let x;                  // Undefined
let empty = null;       // Null
let big = 12345678901234567890n; // BigInt
let id = Symbol("id");  // Symbol

🧩 2. Reference (Non-Primitive) Types

• Object – Collection of key-value pairs
• Array – Ordered list of values
• Function – A block of code that can be called
• Date, RegExp, Error – Built-in object types

let person = { name: "Alice", age: 30 }; // Object
let colors = ["red", "green", "blue"];   // Array
function greet() {
    console.log("Hello!");
}                                       // Function

📊 3. Type Checking with typeof

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

typeof "hello"    // "string"
typeof 42         // "number"
typeof true       // "boolean"
typeof undefined  // "undefined"
typeof null       // "object" (quirk in JS!)
typeof {}         // "object"
typeof []         // "object"
typeof function() {}  // "function"

🧠 Summary

JavaScript has 8 basic data types:

• String
• Number
• Boolean
• Undefined
• Null
• BigInt
• Symbol
• Object