Pick type in Typescript - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Pick type example?

Consider the following TypeScript code using the Pick utility type. What is the type of picked and what will be logged?

Typescript

interface User {
  id: number;
  name: string;
  age: number;
  email: string;
}

const user: User = { id: 1, name: "Alice", age: 30, email: "[e-mail]" };

type UserNameAndEmail = Pick<User, "name" | "email">;

const picked: UserNameAndEmail = { name: "Alice", email: "[e-mail]" };

console.log(picked);

A {"age": 30, "email": "[e-mail]"}

B {"id": 1, "name": "Alice"}

C TypeScript compilation error due to missing properties

D {"name": "Alice", "email": "[e-mail]"}

💡 Hint

Pick creates a new type by selecting only the specified keys from the original type.

The Pick type creates a new type with only the keys 'name' and 'email' from User. So the object 'picked' must have only those two properties. The console.log outputs the object with those properties.

🧠 Conceptual

intermediate

Which statement about Pick type is true?

Choose the correct statement about the TypeScript Pick utility type.

A Pick creates a new type by excluding specified keys from the original type.

B Pick can only be used with primitive types, not interfaces.

C Pick creates a new type by selecting specified keys from the original type.

D Pick modifies the original type by adding new keys.

💡 Hint

Think about what Pick does to the keys of a type.

Pick creates a new type by selecting only the keys you specify from the original type. It does not exclude keys or modify the original type.

🔧 Debug

advanced

Why does this Pick type usage cause an error?

Given this code, why does TypeScript raise an error?

Typescript

interface Product {
  id: number;
  name: string;
  price: number;
}

type ProductNameAndStock = Pick<Product, "name" | "stock">;

const product: ProductNameAndStock = { name: "Book", stock: 10 };

A "stock" is not a key of Product, so Pick causes a type error.

B The object is missing the "price" property, causing an error.

C Pick cannot be used with more than one key.

D The object must include all keys of Product, Pick does not change that.

💡 Hint

Check if all keys in Pick exist in the original interface.

The key "stock" does not exist in Product, so Pick is invalid and causes a type error.

📝 Syntax

advanced

Which option correctly uses Pick to select keys?

Select the correct TypeScript syntax to create a type with only the "title" and "author" keys from the interface Book.

Typescript

interface Book {
  title: string;
  author: string;
  pages: number;
  published: Date;
}

A type BookSummary = Pick<Book, "title", "author">;

B type BookSummary = Pick<Book, "title" | "author">;

C type BookSummary = Pick<Book, ["title", "author"]>;

D type BookSummary = Pick<Book, { title: string; author: string }>;

💡 Hint

Pick takes two parameters: the type and a union of keys as string literals.

Pick expects the second parameter to be a union of keys as string literals separated by |, not multiple parameters or arrays or objects.

🚀 Application

expert

How many keys are in the resulting type?

Given this code, how many keys does the type PartialPick have?

Typescript

interface Settings {
  theme: string;
  notifications: boolean;
  autoSave: boolean;
  version: number;
}

type PartialPick = Pick<Settings, keyof Settings>;

A 4 keys

B 3 keys

C 2 keys

D 0 keys

💡 Hint

keyof Settings returns all keys of Settings.

keyof Settings returns all keys: "theme", "notifications", "autoSave", "version". Pick with all keys returns a type with all 4 keys.