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Chapter XX · Classes

extends

The `extends` keyword is used in class declarations to create a child class that inherits from a parent class.

01 How It Works

Think of building a specialized sports car model that extends standard base car manufacturing specs.

Under the hood, `extends` sets up the prototype chain link between the child constructor and parent constructor.

example.js
class Animal {
  eat() { console.log("Eating"); }
}
class Dog extends Animal {
  bark() { console.log("Woof"); }
}

  1. 1. Declare a child class using `class Child extends Parent`.

  2. 2. Call `super()` inside the child constructor.

  3. 3. Inherit all parent class methods and properties.

02 Practical Example

Here is how you might see this concept applied in real-world code:

practical.js
class Shape {
  constructor(color) { this.color = color; }
}
class Circle extends Shape {
  radius = 5;
}

Key Takeaway

The `extends` keyword provides clean syntax for class-based inheritance hierarchies.

Related Concepts