ConstructorParameters type in Typescript - Mini Project: Build & Apply

Using the ConstructorParameters Type in TypeScript

📖 Scenario: You are building a simple system to manage books in a library. Each book has a title and an author. You want to create a class for books and then use TypeScript's ConstructorParameters type to extract the types of the constructor parameters for reuse.

🎯 Goal: Learn how to use the ConstructorParameters utility type to get the types of a class constructor's parameters and use them to type a function parameter.

📋 What You'll Learn

Create a Book class with a constructor that takes title and author as strings

Create a type alias BookParams using ConstructorParameters for the Book class

Write a function createBook that takes BookParams as its parameter and returns a new Book instance

Print the created book's title and author

💡 Why This Matters

🌍 Real World

Extracting constructor parameter types helps when you want to reuse those types elsewhere, like in factory functions or dependency injection.

💼 Career

Understanding TypeScript utility types like <code>ConstructorParameters</code> is useful for writing clean, type-safe code in professional TypeScript projects.

1

Create the Book class

Create a class called Book with a constructor that takes two parameters: title and author, both of type string. Store these parameters as public properties.

Typescript

class Book {
    // Your code here
}

Need a hint?

Use constructor(public title: string, public author: string) {} to create and store the properties.

2

Create the BookParams type alias

Create a type alias called BookParams that uses ConstructorParameters with the typeof Book to get the constructor parameter types.

Typescript

class Book {
    constructor(public title: string, public author: string) {}
}

// Your code here

Need a hint?

Use type BookParams = ConstructorParameters; to extract the constructor parameters.

3

Write the createBook function

Write a function called createBook that takes one parameter named params of type BookParams. The function should return a new Book instance using the spread operator to pass params to the Book constructor.

Typescript

class Book {
    constructor(public title: string, public author: string) {}
}

type BookParams = ConstructorParameters;

// Your code here

Need a hint?

Use return new Book(...params); inside the function to create the book.

4

Create a book and print its details

Call the createBook function with the parameters "The Hobbit" and "J.R.R. Tolkien". Store the result in a variable called myBook. Then print the book's title and author using console.log.

Typescript

class Book {
    constructor(public title: string, public author: string) {}
}

type BookParams = ConstructorParameters;

function createBook(params: BookParams): Book {
    return new Book(...params);
}

// Your code here

Need a hint?

Use console.log(`Title: ${myBook.title}, Author: ${myBook.author}`); to print the details.