Inheritance

In OO languages, we want to stay DRY and avoid getting WET. Inheritance allows us to avoid writing duplicate code. JavaScript classes give us this ability…

class Animal {
    constructor(name){
        this.name = name;
    }     speak(){
        return ${this.name} says “ugh!”;
    }
}  

We can use this animal class and extend (inherit) it to another object. Here’s an example…

class Primate extends Animal {} 
let gorilla = new Primate(‘Bongo’);
console.log(gorilla.name); 

The output would be “Bongo”. We extended the Animal class. This gives us access to all of the functionality within the Animal class. That is how we were able to get access to the name property. Notice that there is no constructor in the Primate class. What if we had one though?

class Primate extends Animal {
    constructor(){}
} 

It would return a reference error because the code is looking to the constructor within the Primate class and not the Animal class. We need it to look to the constructor in the Animal class first. We do this by using the “super” method…

class Primate extends Animal {
    constructor(){
        super();
    }
} 

Our code would still return a reference error because the property value we sent is not going all the way through to the Animal class constructor. We have to send the argument through the super function.

class Primate extends Animal {
    constructor(name){
        super(name);
    }
} 

What if we had a method with the same name in both the Primate class and the Animal class? The secondary class method runs, but if we want the Animal method to run, we use super again…

class Animal {
    constructor(name){
        this.name = name;
    }
    speak(){
        return ${this.name} says;
    } }
class Primate extends Animal {
    constructor(name){
        super(name);
    }
    speak(){
        return super.speak() + “ugh!”;
    } }
let gorilla = new Primate(‘Bongo’);
console.log(gorilla.speak()); 

The output would read, “Bongo says “ugh!”. So we can use inheritance to mix and match functionality and even override if we wish.

Happy Coding!

Clay Hess