Classes & Object-Oriented Programming

TypeScript enhances ES6 classes with access control modifiers, shorthand constructor properties, and abstract base classes.

1. Access Modifiers (`public`, `private`, `protected`)

2. Concise Parameter Properties Shorthand

Instead of declaring fields separately and assigning them inside the constructor, prefix constructor parameters with access modifiers to auto-create fields!

class User {
  public name: string;
  private secretKey: string;

  constructor(name: string, key: string) {
    this.name = name;
    this.secretKey = key;
  }
}

class User {
  // Auto-declares & initializes fields!
  constructor(
    public name: string,
    private secretKey: string
  ) {}
}

3. Abstract Classes (`abstract`)

Abstract classes cannot be instantiated directly with new. They serve as base blueprints for derived child classes:

abstract class PaymentProcessor {
  constructor(public amount: number) {}

  // Abstract method must be implemented by child classes!
  abstract processPayment(): void;
}

class StripeProcessor extends PaymentProcessor {
  processPayment() {
    console.log(`Processing $${this.amount} via Stripe API...`);
  }
}