Learn TypeScript

Quiz

This quiz will test what you have learned about working with classes with TypeScript.

What are the types of the a and b fields in the following class?

class Calculator {
  a = 0;
  b = 0;
}

What is the return type of the add method in the following class?

class Calculator {
  static add(a: number, b: number) {
    return a + b;
  }
}

What is the problem with the following code?

class Calculator {
  constructor (private a = 0, private b = 0) {}
  add() {
    return this.a + this.b;
  }
}
const calc = new Calculator();
calc.a = 1;
calc.b = 2;
calc.add();

What will be output to the console after the following code is executed? Will any type errors occur?

abstract class Animal {
  constructor (public name: string) {}
  protected log(message: string) {
    console.log(message);
  }
}
class Dog extends Animal {
  bark() {
    this.log(this.name + " Bark");
  }
}
const dog = new Dog("Fudge");
dog.bark();

Will the following code raise a type error?

class Logger {
  static log(message: any): void
  static log(message: string, category: string): void
  static log(message: any, category?: string): void {
    console.log(message, category);
  }
}
Logger.log({name: "Bob"});

Learn TypeScript

Quiz

Quiz

Extending classes

Introduction