How to fix Abstract members must be in abstract class in TypeScript

// ❌ Wrong - regular class with abstract member
class Animal {
  abstract makeSound(): void;
}

// ✅ Correct - abstract class with abstract member
abstract class Animal {
  abstract makeSound(): void;
}

abstract class Animal {
  abstract makeSound(): void;
  abstract move(): void;
}

class Dog extends Animal {
  makeSound(): void {
    console.log("Woof");
  }

  move(): void {
    console.log("Running on four legs");
  }
}

const dog = new Dog(); // ✅ Now this works
dog.makeSound(); // "Woof"

abstract class Animal {
  abstract makeSound(): void;
  abstract move(): void;
}

// ❌ Error - doesn't implement move() and isn't abstract
class Dog extends Animal {
  makeSound(): void {
    console.log("Woof");
  }
}

// ✅ Correct - also abstract since move() not implemented
abstract class Dog extends Animal {
  makeSound(): void {
    console.log("Woof");
  }
}

class Labrador extends Dog {
  move(): void {
    console.log("Running fast");
  }
}

// Before - incorrect abstract class
class Car {
  abstract startEngine(): void;
}

// After - concrete implementation
class Car {
  startEngine(): void {
    console.log("Engine started");
  }
}