CODEWITHSUNDEEP
javascript
TheHedge
TheHedge

Reputation: 127

Add functions to super class that will be used by the subclass also

I'm pretty new to JS and it seems everything seems to have so many ways to do that will make you confused.Anyways this is what I am trying to do:

//SuperClass
function Animal(name, origin, type) {
  this.name = name;
  this.origin = origin;
  this.type = type;

  //Some function that does something
  this.makeSound = function() {
    return "foo";
  }
}

function Mamal(name, origin, type, weight, height) {
  Animal.call(this, name, origin, type);
  this.weight = weight;
  this.height = height;

  this.makeSound = function() {
    return "I am a Mamal";
  }
}

So the question is how would I add a function to the Animal class AFTER it has been declared so that the Mamal class (or whatever subclass) also inherits it and can use it.

Upvotes: 0

Views: 725

Answers (1)

amyloula
amyloula

Reputation: 1566

If I understand your question correctly, what you actually want to achieve is that the Mamal class inherits methods from the Animal class? As in your question you have referred to them as Classes, I have provided an example with classes, rather than functions.

If so, you can declare Mamal like so:

class Mamal extends Animal {
    constructor(weight, height) {
        super();
        this.weight = weight;
        this.height = height;
    }

    // if you want to execute the Animal implementation of makeSound
    makeSound() {
        return super.makeSound();
    }

    // if you want to overwrite the Animal implementation of makeSound
    makeSound() {
        return "I am a mammal";
    }
}

The extends keyword is used in class declarations or class expressions to create a class as a child of another class.

Sub classing with extends Super class calls with super

Update

Find the prototypal inheritance alternative here:

function Animal(name, origin, type) {
    this.name = name;
    this.origin = origin;
    this.type = type;
}

Animal.prototype.makeSound = function () {
    return "foo";
};

function Mammal(weight, height) {
    this.weight = weight;
    this.height = height;
    Animal.call(this); // call super constructor.
}

Mammal.prototype = Object.create(Animal.prototype); //inherit the Animal object through the prototype chain

Mammal.prototype.makeSound = function () {
    return "I am a mammal";
}; //Overwrite the makeSound method inherited from Animal

const cheetah = new Animal('cheetah', 'Africa', 'mammal');
cheetah.makeSound();
//foo

const mammal = new Mammal('100kg', '1m');
mammal.makeSound();
//I am a mammal

Upvotes: 1

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