Quiz

1.

Consider the following code:

type Readings = {
  readonly date: Date;
  readonly values: number[];
}
const readings: Readings = {
  date: new Date(),
  values: [4, 3, 5]
}
readings.values.push(1);

Does a type error occur on the assignment on the last line?

2.

Consider the following code:

type Person = {
  firstName: string;
  surname: string;
  profile: {
    rating: string;
  }
}
const bob: Readonly<Person> = {
  firstName: "Bob",
  surname: "Keel",
  profile: {
    rating: "medium"
  }
  bob.surname = "Steel";
  bob.profile.rating = "high";
};

Do any type errors occur on the surname and rating assignments on the last 2 lines?

3.

Consider the following code:

type Person = {
  firstName: string;
  surname: string;
}
const bob: Readonly<Person> = {
  firstName: "Bob",
  surname: "Keel"
};
bob.surname = "Smith";
console.log(bob.surname);

What will be output to the console when the transpiled JavaScript is executed?

4.

Consider the following code:

const bob = {
  name: {
    firstName: "Bob",
    surname: "Keel"
  },
  profile: {
    rating: "medium"
  }
} as const;
bob.name.surname = "Smith";
bob.profile.rating = "high";

Do any type errors occur on the assignments on the last 2 lines?

5.

Consider the following code:

type Person = {
  name: string;
  profile: {
    level: number;
  }
};
function increaseLevel(person: Readonly<Person>) {
  person.profile.level++;
  return person;
}

Do any type errors occur in the function?

6.

Consider the following code:

type Person = {
  firstName: string;
  surname: string;
}
const bob: Readonly<Person> = Object.freeze({
  firstName: "Bob",
  surname: "Keel"
});
bob.surname = "Smith";
console.log(bob.surname);

What will be output to the console when the transpiled JavaScript is executed?

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Quiz

Creating deep immutable types

Introduction