Inheritance

Intermediate~22 min

Inheritance allows classes to inherit properties and methods from parent classes, promoting code reuse and establishing hierarchies.

Basic Inheritance

Output

Click Run to execute your code

Key Concepts:

extends - Creates inheritance relationship
super() - Calls parent constructor
Child inherits ALL parent members
Can override parent methods

Method Overriding

Child classes can override parent methods to provide specific behavior:

class Animal {
    makeSound(): void {
        console.log("Generic sound");
    }
}

class Cat extends Animal {
    makeSound(): void {  // Override
        console.log("Meow!");
    }
}

let cat = new Cat();
cat.makeSound();  // "Meow!"

Common Mistakes

1. Forgetting super() in Constructor

class Animal {
    constructor(public nameAnimal: string) {}
}

class Dog extends Animal {
    constructor(nameAnimal: string, public breed: string) {
        // ✗ Error - must call super() first!
        this.breed = breed;
    }
}

// ✓ Correct
class Dog extends Animal {
    constructor(nameAnimal: string, public breed: string) {
        super(nameAnimal);  // Call parent first
        this.breed = breed;
    }
}

2. Accessing Private Parent Members

class Parent {
    private secret = "hidden";
}

class Child extends Parent {
    reveal() {
        console.log(this.secret);  // ✗ Error! Private
    }
}

// ✓ Use protected instead
class Parent {
    protected secret = "hidden";
}

Best Practice: Favor composition over deep inheritance hierarchies. Keep hierarchies shallow (2-3 levels max).

Summary

Use extends for inheritance
Call super() in child constructor
Child inherits all parent members
Override methods for specific behavior
Use protected for inheritance-friendly members

Previous ← Access Modifiers

Next Abstract Classes →