How to override a base class constructor in Javascript

Question

The Udacity ES6 training has a question about overriding a base class constructor. I've got a solution but Udacity doesn't let me get away with it.

The assignment is: Create a Bicycle subclass that extends the Vehicle class. The Bicycle subclass should override Vehicle's constructor function by changing the default values for wheels from 4 to 2 and horn from 'beep beep' to 'honk honk'.

class Vehicle {
    constructor(color = 'blue', wheels = 4, horn = 'beep beep') {
        this.color = color;
        this.wheels = wheels;
        this.horn = horn;
    }

    honkHorn() {
        console.log(this.horn);
    }
}

// your code here


/* tests
const myVehicle = new Vehicle();
myVehicle.honkHorn(); // beep beep
const myBike = new Bicycle();
myBike.honkHorn(); // honk honk
*/

The solution that I come up with is:

class Bicycle extends Vehicle {
    constructor(wheels, horn){
        super(wheels, horn)
        this.wheels = 2
        this.horn = "honk honk" 
    }

    honkHorn(){
        super.honkHorn()
    }

}

But that is not good enough And I do not understand why that is. The feedback I got is:

Your Bicycles constructor doesn't set default values for color, wheels, and horn

I think the exercice is expecting you to set default values for every constructor arguments even in your Bicycle class. Something like this: jsfiddle.net/nf570m4k — briosheje
– briosheje, Commented Apr 19, 2019 at 10:10
extending the above answer (in your Bicycle) constructor(wheels = 2, horn = 'tring tring') — 1565986223
– 1565986223, Commented Apr 19, 2019 at 10:16

arizafar · Accepted Answer · 2019-04-19 11:11:28Z

5

you should not be using

    this.wheels = 2
    this.horn = "honk honk"

when already overriding these in super constructor.

class Vehicle {
	constructor(color = 'blue', wheels = 4, horn = 'beep beep') {
		this.color = color;
		this.wheels = wheels;
		this.horn = horn;
	}

	honkHorn() {
		console.log(this.horn);
	}
}

class Bicycle extends Vehicle {
	constructor(wheels = 2, horn = 'honk honk') {
		super(undefined, wheels, horn);
	}

	honkHorn() {
		super.honkHorn()
	}

}

let by = new Bicycle();
by.honkHorn();

edited Apr 19, 2019 at 11:11

answered Apr 19, 2019 at 10:24

arizafar

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2 Comments

arizafar Over a year ago

have you tried removing ` this.wheels = 2 this.horn = "honk honk" ` from Bycible constructor. @Edwin

Amit L. Over a year ago

You should also not set color to be undefined. It will not allow you to submit with color set to undefined. Just use:

class Bicycle extends Vehicle {    constructor(color, wheels = 2, horn = "honk honk") {    super(color, wheels, horn);  }

Edwin · Accepted Answer · 2019-04-19 13:31:58Z

0

class Bicycle extends Vehicle {
    constructor(wheels =2, horn= "honk honk"){
        super(undefined, wheels, horn)
    }

    honkHorn(){
        super.honkHorn()
    }

}

then for the test I added:

const yourBike = new Bicycle(3, "tring tring")

Although other options did provide the right answers for the test cases described in the question. By adding this extra test I found out that overriding a base class constructor is not possible from super nor from this.wheels (as was my first attempt).

However Udacity does not accept it......

edited Apr 19, 2019 at 13:31

answered Apr 19, 2019 at 11:33

Edwin

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Comments

Abishek · Accepted Answer · 2023-05-05 10:25:27Z

0

class Vehicle {
    constructor(color = 'blue', wheels = 4, horn = 'beep beep') {
        this.color = color;
        this.wheels = wheels;
        this.horn = horn;
    }

    honkHorn() {
        console.log(this.horn);
    }
}


class Bicycle extends Vehicle {
    constructor(color,wheels = 2,horn = 'honk honk'){
        super(color,wheels,horn);
    }
}

you need not want to call honkHorn() in the child, it automatically calls from the parent.

const myVehicle = new Vehicle();
myVehicle.honkHorn(); // beep beep
const myBike = new Bicycle();
myBike.honkHorn(); // honk honk

edited May 5, 2023 at 10:25

answered May 4, 2023 at 9:25

Abishek

11 bronze badge

1 Comment

Community Over a year ago

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