Polymorphism

JavaScript · Unit 13: Inheritance

Full plan
JavaScript
10 exercises

Polymorphism means objects of different classes answer the same method, each in its own way. Whoever uses them doesn't ask which is which: it just calls the method.

Here the loop treats every notice the same, and each one gets sent its own way.

class Notice {
  send(t) {
    return `Notice: ${t}`;
  }
}
class Sms extends Notice {
  send(t) {
    return `SMS: ${t}`;
  }
}
class Email extends Notice {
  send(t) {
    return `Email: ${t}`;
  }
}
const notices = [
  new Sms(),
  new Email(),
];
for (const n of notices) {
  console.log(n.send("Hi"));
}

Prints

SMS: Hi
Email: Hi

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. Predict the output
What does this code print?
2. Predict the output
Paying by card adds a 10% fee. How much is charged in total?
3. Predict the output
What does this code print?
4. Complete the code
Fill in the blank to ask whether p is a Payment.
5. Find the bug
This program should print true. Which line has the bug?
6. Predict the output
Look at the order of the questions. What does it print?
7. Multiple choice
Noah wrote this function. Every new animal forces him to add another else if. What does polymorphism suggest?
8. Predict the output
NoFunds doesn't define name. What does it print?
9. Put the lines in order
Put in order the program that throws a SoldOut error and, when it catches it, prints its message only if it's of that kind.
10. Predict the output
The line at the movies. What does it print?

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