fix: remove access modifiers, use native #private fields

BREAKING CHANGE: Access modifiers exercise completely removed

- Delete 02.access-modifiers exercise entirely (public/private/protected
  keywords removed from curriculum)
- Renumber exercises: interfaces-and-classes → 02, inheritance → 03,
  polymorphism → 04, composition-vs-inheritance → 05
- Integrate #private fields (native JavaScript private) into 01.classes
  exercise as the preferred encapsulation pattern
- Update all code examples to use #private instead of TypeScript private
- Update README and descriptions to reflect new structure

Author: kentcdodds

README.md

@@ -4,7 +4,7 @@
     Build robust applications with classes, inheritance, and design patterns
   </strong>
   <p>
-    Learn classes, access modifiers, inheritance, polymorphism, and when to choose composition over inheritance.
+    Learn classes, inheritance, polymorphism, and when to choose composition over inheritance.
   </p>
 </div>
 

exercises/01.classes/02.problem.constructors/README.mdx

@@ -18,18 +18,47 @@ class User {
 }
 ```
 
+## Private Fields
+
+JavaScript has native private fields using the `#` prefix:
+
+```ts
+class BankAccount {
+	#balance: number = 0 // Truly private - not accessible outside the class
+
+	deposit(amount: number) {
+		this.#balance += amount
+	}
+}
+
+const account = new BankAccount()
+account.#balance // ❌ Error! Private field not accessible
+```
+
 🐨 Open <InlineFile file="index.ts" /> and:
 
-1. Refactor classes to use parameter properties
+1. Create classes using parameter property shorthand
 2. Use default parameter values
-3. Make some parameters optional
+3. Use `#` prefix for fields that should be private
+
+💰 Parameter property shorthand:
+
+```ts
+constructor(public name: string, public email: string) {}
+```
 
-💰 Parameter property syntax:
+💰 Private field syntax:
 
 ```ts
-constructor(public name: string, private age: number = 0) {}
+class Counter {
+	#count: number = 0
+
+	increment() {
+		this.#count++
+	}
+}
 ```
 
-📜 [TypeScript Handbook - Parameter Properties](https://www.typescriptlang.org/docs/handbook/2/classes.html#parameter-properties)
+📜 [MDN - Private class features](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes/Private_class_fields)
 
 🐨 Once you've completed the exercise, run `node index.ts` in the playground to test your work!

exercises/01.classes/02.problem.constructors/index.ts

@@ -1,20 +1,22 @@
 // Constructor Patterns
 
-// 🐨 Create a User class using parameter properties:
-// - public name: string
-// - public email: string
-// - public role: string (default: 'user')
+// 🐨 Create a User class with these fields:
+// - name: string
+// - email: string
+// - role: string (default: 'user')
+// Use constructor parameter shorthand!
 
 // 🐨 Create a BankAccount class with:
-// - public accountNumber: string
-// - private balance: number (default: 0)
+// - 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
 
-// 🐨 Create a Config class with optional properties:
-// - public host: string (default: 'localhost')
-// - public port: number (default: 3000)
-// - public debug: boolean (default: false)
+// 🐨 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', '[email protected]')

exercises/01.classes/02.solution.constructors/index.ts

@@ -9,17 +9,16 @@ export class User {
 }
 
 export class BankAccount {
-	constructor(
-		public accountNumber: string,
-		private balance: number = 0,
-	) {}
+	#balance: number = 0
+
+	constructor(public accountNumber: string) {}
 
 	deposit(amount: number): void {
-		this.balance += amount
+		this.#balance += amount
 	}
 
 	getBalance(): number {
-		return this.balance
+		return this.#balance
 	}
 }
 
@@ -39,6 +38,7 @@ console.log(`${admin.name} is a ${admin.role}`)
 const account = new BankAccount('12345')
 account.deposit(100)
 console.log(`Balance: $${account.getBalance()}`)
+// account.#balance would be an error - truly private!
 
 const config = new Config()
 const customConfig = new Config('example.com', 8080, true)