JavaScript Data Types

What Are Data Types?

Think of data types like different kinds of containers. You wouldn't put water in a box meant for books, right? JavaScript needs to know what kind of data you're storing so it knows how to work with it.

``` ┌─────────────────────┐ │ JavaScript sees: │ │ │ │ "John" → String │ ← Text │ 25 → Number │ ← Number │ true → Boolean │ ← Yes/No │ [1,2,3] → Array │ ← List │ {...} → Object │ ← Collection └─────────────────────┘ ```

The Main Types You'll Use

### 1. Numbers

Numbers are just... numbers. Whole numbers, decimals, negative numbers - all are numbers.

```javascript const age = 25; const price = 19.99; const temperature = -5; ```

JavaScript doesn't care if it's a whole number or decimal. It's all just a number.

### 2. Strings (Text)

Strings are text. Anything in quotes is a string.

```javascript const name = 'John'; const message = "Hello there"; const greeting = `Hi, ${name}`; ```

You can use single quotes, double quotes, or backticks. They all work the same for basic text. Backticks let you put variables inside.

### 3. Booleans (True or False)

Booleans are simple - just true or false. Like a light switch - it's either on or off.

```javascript const isLoggedIn = true; const hasPermission = false; const isAdult = age >= 18; // This becomes true or false ```

### 4. Arrays (Lists)

Arrays are lists of things. Like a shopping list.

```javascript const fruits = ['apple', 'banana', 'orange']; const numbers = [1, 2, 3, 4, 5]; ```

You put items in square brackets, separated by commas.

### 5. Objects (Collections)

Objects store related information together. Like a person's profile.

```javascript const person = { name: 'John', age: 25, city: 'New York' }; ```

You use curly braces and put key-value pairs inside.

How to Check What Type Something Is

Sometimes you need to know what type something is:

```javascript typeof 'hello'; // "string" typeof 42; // "number" typeof true; // "boolean" typeof [1, 2, 3]; // "object" (arrays are objects in JavaScript) ```

A Common Gotcha: Type Mixing

JavaScript sometimes converts types automatically, which can be confusing:

```javascript '5' + 3; // "53" (treats 3 as text, joins them) '5' - 3; // 2 (treats '5' as number, does math) ```

The plus sign joins strings together. Minus, multiply, and divide convert to numbers first.

Real Example: Working with Types

Let's say you're building a user profile:

```javascript // User's name (string) const userName = 'John';

// User's age (number) const userAge = 25;

// Is user active? (boolean) const isActive = true;

// User's hobbies (array) const hobbies = ['reading', 'coding', 'gaming'];

// User's address (object) const address = { street: '123 Main St', city: 'New York', zipCode: '10001' }; ```

Each piece of information has a type. JavaScript uses that type to know how to work with it.

Quick Reference

- **Number:** 1, 2.5, -10 - **String:** 'text', "text", `text` - **Boolean:** true, false - **Array:** [1, 2, 3] - **Object:** { key: 'value' }

That's the basics! You'll use these types constantly. Numbers for math, strings for text, booleans for yes/no questions, arrays for lists, objects for collections of related data.