InstanceType type in Typescript - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to get the instance type of the class.

Typescript

class Person {
  name: string;
  constructor(name: string) {
    this.name = name;
  }
}
type PersonInstance = [1]<typeof Person>;

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AInstanceType

BReturnType

CParameters

DConstructorParameters

Attempts:

3 left

💡 Hint

Common Mistakes

Using ReturnType instead of InstanceType

Using Parameters or ConstructorParameters which extract function parameters

The InstanceType type extracts the instance type from a class constructor type.

2fill in blank

medium

Complete the code to create an instance of the class using the instance type.

Typescript

class Car {
  model: string;
  constructor(model: string) {
    this.model = model;
  }
}
type CarInstance = InstanceType<typeof Car>;
const myCar: [1] = new Car('Tesla');

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ACar

Bstring

Ctypeof Car

DCarInstance

Attempts:

3 left

💡 Hint

Common Mistakes

Using the class type Car instead of the instance type alias

Using typeof Car which is the constructor type

The variable myCar should be typed as the instance type of Car, which is CarInstance.

3fill in blank

hard

Fix the error in the code by completing the type alias correctly.

Typescript

class Animal {
  species: string;
  constructor(species: string) {
    this.species = species;
  }
}
type AnimalInstance = [1];

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AInstanceType<typeof Animal>

BReturnType

CInstanceType

Dtypeof Animal

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the class type Animal directly instead of typeof Animal

Using ReturnType which is for functions

The InstanceType utility requires a constructor type, so we must pass typeof Animal inside the angle brackets.

4fill in blank

hard

Fill both blanks to create a type alias for the instance type and declare a variable of that type.

Typescript

class Book {
  title: string;
  constructor(title: string) {
    this.title = title;
  }
}
type [1] = [2]<typeof Book>;
const myBook: BookInstance = new Book('1984');

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ABookInstance

BInstanceType

CReturnType

DBookType

Attempts:

3 left

💡 Hint

Common Mistakes

Using ReturnType instead of InstanceType

Naming the alias incorrectly

The type alias should be named BookInstance and use InstanceType with typeof Book.

5fill in blank

hard

Fill all three blanks to create an instance type alias, declare a variable, and access a property.

Typescript

class User {
  username: string;
  constructor(username: string) {
    this.username = username;
  }
}
type [1] = [2]<typeof User>;
const user: UserInstance = new User('alice');
const name: string = user.[3];

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AUserInstance

BInstanceType

Cusername

DuserName

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect property name userName with uppercase N

Not using InstanceType with typeof User

The alias is UserInstance, using InstanceType with typeof User. The property to access is username.