feat: enhance class examples with test cases and improve README documentation

Author: kentcdodds

exercises/01.classes/01.problem.class-basics/index.ts

@@ -5,19 +5,23 @@
 // - Constructor to initialize both
 // - Method: getDescription() returns "Product: {name} - ${price}"
 
+// Test Product
+// const laptop = new Product('Laptop', 999.99)
+// const mouse = new Product('Mouse', 29.99)
+// console.log(laptop)
+// console.log(mouse)
+
 // 🐨 Create a ShoppingCart class with:
 // - Field: items (Array<Product>)
 // - Constructor to initialize empty items array
 // - Method: addItem(product: Product) adds to items
 // - Method: getTotal() returns sum of all product prices
 
-// Test your classes
-// const laptop = new Product('Laptop', 999.99)
-// const mouse = new Product('Mouse', 29.99)
+// Test ShoppingCart
 // const cart = new ShoppingCart()
 // cart.addItem(laptop)
 // cart.addItem(mouse)
 // console.log(cart.getTotal())
+// console.log(cart)
 
-// 🐨 Export your classes so we can verify your work
-// 💰 Export the classes you created
+// export { Product, ShoppingCart }

exercises/01.classes/02.problem.private-fields-and-defaults/README.mdx

@@ -9,16 +9,21 @@ JavaScript has native private fields using the `#` prefix. These fields are
 truly private—they can only be accessed inside the class:
 
 ```ts
-class BankAccount {
-	#balance: number = 0 // Truly private - not accessible outside the class
+class Counter {
+	#count: number = 0 // Truly private - not accessible outside the class
 
-	deposit(amount: number) {
-		this.#balance += amount
+	increment() {
+		this.#count++
+	}
+
+	getValue() {
+		return this.#count
 	}
 }
 
-const account = new BankAccount()
-account.#balance // ❌ Error! Private field not accessible
+const counter = new Counter()
+counter.increment()
+counter.#count // ❌ Error! Private field not accessible
 ```
 
 Private fields enable **encapsulation**—hiding internal implementation details
@@ -30,18 +35,20 @@ your code more maintainable.
 Constructors can use default parameter values to make some parameters optional:
 
 ```ts
-class User {
-	name: string
-	role: string
-
-	constructor(name: string, role: string = 'user') {
-		this.name = name
-		this.role = role
+class Car {
+	make: string
+	model: string
+	year: number
+
+	constructor(make: string, model: string, year: number = 2024) {
+		this.make = make
+		this.model = model
+		this.year = year
 	}
 }
 
-const user = new User('Alice') // role defaults to 'user'
-const admin = new User('Bob', 'admin') // role explicitly set
+const newCar = new Car('Toyota', 'Camry') // year defaults to 2024
+const oldCar = new Car('Ford', 'Mustang', 1965) // year explicitly set
 ```
 
 🐨 Open <InlineFile file="index.ts" /> and:

exercises/01.classes/02.problem.private-fields-and-defaults/index.ts

@@ -6,25 +6,34 @@
 // - role: string (default: 'user')
 // Initialize fields in the constructor
 
+// Test User
+// const user = new User('Alice', 'alice@example.com')
+// const admin = new User('Bob', 'bob@example.com', 'admin')
+// console.log(user)
+// console.log(admin)
+
 // 🐨 Create a BankAccount class with:
 // - accountNumber: string
 // - #balance: number (private field, default: 0)
 // - Method: deposit(amount: number)
 // - Method: getBalance() returns the balance
 // 💰 #balance is a private field - can only be accessed inside the class
 
+// Test BankAccount
+// const account = new BankAccount('12345')
+// account.deposit(100)
+// console.log(account)
+// console.log(account.getBalance())
+
 // 🐨 Create a Config class with optional default values:
 // - host: string (default: 'localhost')
 // - port: number (default: 3000)
 // - debug: boolean (default: false)
 
-// Test
-// const user = new User('Alice', 'alice@example.com')
-// const admin = new User('Bob', 'bob@example.com', 'admin')
-// const account = new BankAccount('12345')
-// account.deposit(100)
+// Test Config
 // const config = new Config()
 // const customConfig = new Config('example.com', 8080, true)
+// console.log(config)
+// console.log(customConfig)
 
-// 🐨 Export your classes so we can verify your work
-// 💰 Export the classes you created
+// export { User, BankAccount, Config }

exercises/02.interfaces-and-classes/01.problem.implementing-interfaces/index.ts

@@ -8,16 +8,19 @@
 // - Constructor that takes cardNumber
 // - Implement pay(amount: number) returns "Paid $${amount} with credit card ${cardNumber}"
 
+// Test CreditCard
+// const creditCard = new CreditCard('1234-5678-9012-3456')
+// console.log(creditCard.pay(100))
+// console.log(creditCard)
+
 // 🐨 Create a PayPal class that implements PaymentMethod:
 // - Field: email (string)
 // - Constructor that takes email
 // - Implement pay(amount: number) returns "Paid $${amount} with PayPal ${email}"
 
-// Test your classes
-// const creditCard = new CreditCard('1234-5678-9012-3456')
+// Test PayPal
 // const paypal = new PayPal('user@example.com')
-// console.log(creditCard.pay(100))
 // console.log(paypal.pay(50))
+// console.log(paypal)
 
-// 🐨 Export your classes so we can verify your work
-// 💰 Export the classes you created
+// export { CreditCard, PayPal }

exercises/02.interfaces-and-classes/02.problem.programming-to-abstractions/index.ts

@@ -8,21 +8,26 @@
 // - Constructor that takes cardNumber
 // - Implement pay(amount: number) returns "Paid $${amount} with credit card ${cardNumber}"
 
+// Test CreditCard
+// const creditCard = new CreditCard('1234-5678-9012-3456')
+// console.log(creditCard)
+
 // 🐨 Create a PayPal class implementing PaymentMethod:
 // - Field: email (string)
 // - Constructor that takes email
 // - Implement pay(amount: number) returns "Paid $${amount} with PayPal ${email}"
 
+// Test PayPal
+// const paypal = new PayPal('user@example.com')
+// console.log(paypal)
+
 // 🐨 Create a processPayment function:
 // - Parameters: method (PaymentMethod), amount (number)
 // - Returns: string
 // - Calls method.pay(amount)
 
-// Test your code
-// const creditCard = new CreditCard('1234-5678-9012-3456')
-// const paypal = new PayPal('user@example.com')
+// Test processPayment
 // console.log(processPayment(creditCard, 100))
 // console.log(processPayment(paypal, 50))
 
-// 🐨 Export your classes and function so we can verify your work
-// 💰 Export the classes and function you created
+// export { CreditCard, PayPal, processPayment }

exercises/03.inheritance/01.problem.extends/index.ts

@@ -9,18 +9,21 @@
 // - Constructor that takes color and radius
 //   - Call super(color) to initialize parent
 
+// Test Circle
+// const circle = new Circle('red', 5)
+// console.log(circle.color) // ✅ Should work - inherited from Shape
+// console.log(circle.radius) // ✅ Should work - defined in Circle
+// console.log(circle)
+
 // 🐨 Create a Rectangle class that extends Shape:
 // - Fields: width (number), height (number)
 // - Constructor that takes color, width, and height
 //   - Call super(color) to initialize parent
 
-// Test your classes
-// const circle = new Circle('red', 5)
+// Test Rectangle
 // const rectangle = new Rectangle('blue', 10, 20)
-// console.log(circle.color) // ✅ Should work - inherited from Shape
-// console.log(circle.radius) // ✅ Should work - defined in Circle
 // console.log(rectangle.color) // ✅ Should work - inherited from Shape
 // console.log(rectangle.width, rectangle.height) // ✅ Should work
+// console.log(rectangle)
 
-// 🐨 Export your classes so we can verify your work
-// 💰 Export the classes you created
+// export { Shape, Circle, Rectangle }

exercises/03.inheritance/02.problem.method-overriding/index.ts

@@ -10,16 +10,19 @@
 // - Constructor that takes color and radius
 // - Override getArea() to return Math.PI * radius ** 2
 
+// Test Circle
+// const circle = new Circle('red', 5)
+// console.log(circle.getArea()) // Should print ~78.54
+// console.log(circle)
+
 // 🐨 Create a Rectangle class that extends Shape:
 // - Fields: width (number), height (number)
 // - Constructor that takes color, width, and height
 // - Override getArea() to return width * height
 
-// Test your classes
-// const circle = new Circle('red', 5)
+// Test Rectangle
 // const rectangle = new Rectangle('blue', 10, 20)
-// console.log(circle.getArea()) // Should print ~78.54
 // console.log(rectangle.getArea()) // Should print 200
+// console.log(rectangle)
 
-// 🐨 Export your classes so we can verify your work
-// 💰 Export the classes you created
+// export { Shape, Circle, Rectangle }

exercises/04.polymorphism/01.problem.substitutability/index.ts

@@ -8,19 +8,25 @@
 // 🐨 Create an AudioFile class that extends MediaFile:
 // - Override play() to return "Playing audio: {filename}"
 
+// Test AudioFile
+// const audio = new AudioFile('song.mp3')
+// console.log(audio)
+
 // 🐨 Create a VideoFile class that extends MediaFile:
 // - Override play() to return "Playing video: {filename}"
 
+// Test VideoFile
+// const video = new VideoFile('movie.mp4')
+// console.log(video)
+
 // 🐨 Create a MediaPlayer class with:
 // - Method: playFile(media: MediaFile) returns string
 //   - Calls media.play() and returns the result
 
-// Test polymorphism
-// const audio = new AudioFile('song.mp3')
-// const video = new VideoFile('movie.mp4')
+// Test MediaPlayer (polymorphism)
 // const player = new MediaPlayer()
 // console.log(player.playFile(audio)) // Should work - AudioFile is substitutable for MediaFile
 // console.log(player.playFile(video)) // Should work - VideoFile is substitutable for MediaFile
+// console.log(player)
 
-// 🐨 Export your classes so we can verify your work
-// 💰 Export the classes you created
+// export { MediaFile, AudioFile, VideoFile, MediaPlayer }

exercises/05.composition-vs-inheritance/01.problem.when-to-use/index.ts

@@ -8,24 +8,30 @@
 // - Extends Logger
 // - Override log() to print "File Log: {message}"
 
+// Test FileLogger
+// const fileLogger = new FileLogger()
+// fileLogger.log('File system initialized')
+// console.log(fileLogger)
+
 // 🐨 Create a ConsoleLogger class using INHERITANCE (is-a):
 // - Extends Logger
 // - Override log() to print "Console Log: {message}"
 
+// Test ConsoleLogger
+// const consoleLogger = new ConsoleLogger()
+// consoleLogger.log('Console ready')
+// console.log(consoleLogger)
+
 // 🐨 Create an EmailService class using COMPOSITION (has-a):
 // - Field: #logger (Logger) - private field
 // - Constructor that takes a Logger
 // - Method: sendEmail(to: string, subject: string) returns void
 //   - Uses this.#logger.log() to log the email action
 //   - Prints "Sending email to {to}: {subject}"
 
-// Test your code
-// const fileLogger = new FileLogger()
-// const consoleLogger = new ConsoleLogger()
+// Test EmailService
 // const emailService = new EmailService(fileLogger)
-// fileLogger.log('File system initialized')
-// consoleLogger.log('Console ready')
 // emailService.sendEmail('user@example.com', 'Welcome')
+// console.log(emailService)
 
-// 🐨 Export your classes so we can verify your work
-// 💰 Export the classes you created
+// export { Logger, FileLogger, ConsoleLogger, EmailService }