Object-Oriented JavaScript - Third Edition

Subclassing

So far, we discussed how to declare classes and the types of members classes can support. A major use of a class is to serve as a template to create other subclasses. When you create a child class from a class, you derive properties of the parent class and extend the parent class by adding more features of its own.

Let's look at the following de facto example of inheritance:

    class Animal {  
      constructor(name) { 
        this.name = name; 
      } 
        speak() { 
        console.log(this.name + ' generic noise'); 
      } 
    } 
    class Cat extends Animal { 
      speak() { 
        console.log(this.name + ' says Meow.'); 
      } 
    } 
    var c = new Cat('Grace');  
    c.speak();//"Grace says Meow." 

Here, Animal is the base class and the Cat class is derived from the class Animal. The extend clause allows you to ...