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TypeScript ThisParameterType<Type> Utility Type
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TypeScript InstanceType<Type> Utility Type

Last Updated : 24 Apr, 2025
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In this article, we are going to learn about InstanceType<Type> Utility Type in Typescript. TypeScript is a popular programming language used for building scalable and robust applications. In TypeScript, the InstanceType<Type> utility type is used to extract the instance type of a constructor function or class type. It allows you to infer the type of instances that can be created from a constructor or class.

Syntax

type T1 = InstanceType<Type>;

Parameters

  • Type: This is the type parameter that represents the constructor function or class type from which you want to extract the instance type.
  • T1: This is the name of the utility type that extracts the instance type.

Example 1

In this example,

  • We have a Person class with a constructor that takes a name and an age.
  • We use InstanceType<typeof Person> to extract the instance type of the Person class, which is equivalent to { name: string; age: number; }.
  • We create an instance of Person using new Person("Alice", 30) and assign it to the person variable.
  • TypeScript infers that person is of type PersonInstance, which allows us to access the name and age properties of the person object with type safety.
JavaScript 
class Person {     constructor(public name: string, public age: number) { } }  type PersonInstance = InstanceType<typeof Person>;  const person: PersonInstance = new Person("Alice", 30);  console.log(person.name); // "Alice" console.log(person.age); // 30

Output

z22

Example 2

In this example,

  • We have a Product class with a constructor that takes a name and a price.
  • We also have a ShoppingCart class that can hold instances of Product.
  • InstanceType<typeof Product> is used to specify the type of products that can be added to the shopping cart.
  • We create instances of Product (e.g., laptop and smartphone) and an instance of ShoppingCart (e.g., cart).
  • We add products to the cart using the addItem method.
  • We calculate the total price of the items in the cart using the getTotalPrice method
JavaScript 
class Product {     constructor(public name: string, public price: number) { } }  class ShoppingCart {     private items: InstanceType<typeof Product>[] = [];      addItem(product: InstanceType<typeof Product>): void {         this.items.push(product);     }      getTotalPrice(): number {         return this.items.reduce((total, product                 ) => total + product.price, 0);     } }  // Create instances of Product const laptop = new Product("Laptop", 1000); const smartphone = new Product("Smartphone", 500);  // Create an instance of ShoppingCart const cart = new ShoppingCart();  // Add products to the cart cart.addItem(laptop); cart.addItem(smartphone);  // Get the total price of the items in the cart const totalPrice = cart.getTotalPrice();  // Output: Total Price: $1500 console.log(`Total Price: $${totalPrice}`);

Output

z23

Reference: https://www.typescriptlang.org/docs/handbook/utility-types.html#instancetypetype




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TypeScript ThisParameterType<Type> Utility Type
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