extends

JavaScript · Unit 13: Inheritance

Full plan
JavaScript
10 exercises

Sometimes a class is a more specific version of another: a dog is an animal. With extends, the child class gets everything from the parent class without copying it: its constructor and its methods.

Dog writes nothing between its braces, and it can still eat.

class Animal {
  constructor(name) {
    this.name = name;
  }
  eat() {
    return `${this.name} eats`;
  }
}
class Dog extends Animal {}
const rex = new Dog("Rex");
console.log(rex.eat());

Prints

Rex eats

The rest of the explanation is in the lesson, which is part of the full plan.

Exercises in this lesson

You do them in the app, which checks them on the spot and explains why.

1. Complete the code
Fill in the blank so Scooter is a child class of Vehicle.
2. Predict the output
What does this code print?
3. Multiple choice
Savings was written like this: class Savings extends Account {}. What does an object made with new Savings(100) have?
4. Predict the output
What does this code print?
5. Predict the output
Cat and Dog are children of the same parent. What does it print?
6. Find the bug
This program should print "Rayo drifts". Which line has the bug?
7. Predict the output
What does this code print?
8. Put the lines in order
Put the program in order so Kira, a Cat, introduces herself with the method she inherits from Pet.
9. Multiple choice
A store's program has an Employee class. Which one makes sense as a child class of Employee?
10. Predict the output
Some products in the cart are on sale. What does it print?

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