Understanding JavaScript Data Types day 1

🌟 Two Main Categories

JavaScript divides data types into two broad groups:

1️⃣ Primitive types (simple, immutable values)
2️⃣ Non-primitive types (objects, complex structures)

Let’s go through them.
🔹 Primitive Data Types

These are the most basic types — they hold a single value and are immutable (cannot be changed).
✅ Number

For any numeric value, including decimals.

let age = 25;
let price = 99.99;

✅ String

For text, wrapped in single ' or double " quotes.

let name = "Elayaraj";
let message = 'Hello, world!';

✅ Boolean

True or false — used for logic and conditions.

let isActive = true;
let hasAccess = false;

✅ Undefined

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

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

✅ Null

An intentional empty value.

let user = null;

✅ Symbol

A unique and immutable value, often used as an object key (advanced use).

let id = Symbol("uniqueId");

✅ BigInt

For very large integers beyond Number limits.

let bigNumber = 123456789012345678901234567890n;

🔹 Non-Primitive Data Types

These hold collections of values and are mutable.

✅ Object

A collection of key-value pairs.

let person = {
  name: "Elayaraj",
  age: 25
};

✅ Array

An ordered list of values (technically an object).

let fruits = ["apple", "banana", "cherry"];

✅ Function

A reusable block of code (also a type of object).

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

🧠 Why Does This Matter?

Understanding data types helps you:

• Write bug-free code (no type errors)
• Use correct operations (e.g., adding numbers vs. concatenating strings)
• Master type conversions (e.g., turning strings into numbers)

For example:

let x = "5" + 2;  // "52" (string concatenation)
let y = "5" - 2;  // 3   (number subtraction)

🔍 Type Checking

You can check a value’s type using:

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