Multilevel Inheritance

Definition

Multilevel inheritance is a chain of inheritance where class C inherits from class B, which inherits from class A. Each level in the chain adds more specific behavior.

Characteristics

Aspect	Description
Structure	Grandparent → Parent → Child
Complexity	Medium — must understand the full chain
Risk	Fragile base class problem
Depth Limit	Practical limit: 3-5 levels

Example

class Animal {
  constructor(name) {
    this.name = name;
  }
  eat() { console.log(`${this.name} is eating`); }
}

class Mammal extends Animal {
  constructor(name, hasFur = true) {
    super(name);
    this.hasFur = hasFur;
  }
  breathe() { console.log(`${this.name} is breathing`); }
}

class Dog extends Mammal {
  constructor(name, breed) {
    super(name);
    this.breed = breed;
  }
  bark() { console.log(`${this.name} barks!`); }
}

const dog = new Dog("Rex", "Labrador");
dog.eat();     // Inherited from Animal
dog.breathe(); // Inherited from Mammal
dog.bark();    // Own method

Visual Diagram

classDiagram
    class Animal {
        +eat() void
    }

    class Mammal {
        +breathe() void
    }

    class Dog {
        +bark() void
    }

    Animal <|-- Mammal : extends
    Mammal <|-- Dog : extends

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