Pick

Learn how to build one of TypeScript's most fundamental utility types: Pick! 🎯

In this easy-level challenge, you'll implement the built-in Pick<T, K> generic without using the actual Pick utility. This type allows you to create a new type by selecting specific properties from an existing type. It's a cornerstone of TypeScript's type manipulation capabilities and understanding how it works will deepen your knowledge of mapped types and generic constraints.

You'll be constructing a type that picks a set of properties K from type T, creating a new type with only those selected properties. This is incredibly useful for creating partial interfaces or extracting specific fields from larger types.

interface Todo {
title: string
description: string
completed: boolean
}
 
type TodoPreview = MyPick<Todo, 'title' | 'completed'>
 
const todo: TodoPreview = {
title: 'Clean room',
completed: false,
}

Detailed Explanation

To implement the Pick utility type, you need to understand mapped types and the keyof operator.

The solution uses TypeScript's mapped types to iterate over the keys specified in K and extract their corresponding types from T:

type MyPick<T, K extends keyof T> = {
  [Key in K]: T[Key]
}

Let's break this down:

• K extends keyof T ensures that K can only contain keys that actually exist in T
• [Key in K] iterates over each key in K
• T[Key] gets the type of property Key from the original type T