Partial<Type>

INFO

The Partial<Type> utility type is available starting from TypeScript version 2.1. For more information see in TypeScript Handbook, Release Note.

Overview

Partial<Type> is a built in utility type in TypeSCript that constructs a type with all properties of Type set to optional. This utility will return a type that represents all subsets of a given type.

Syntax

type Partial<T> = { [K in keyof T]?: T[K] | undefined };

• Type (T): The type whose properties you want to make optional.

Examples

Example #1

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

type PartialUser = Partial<User>;
// This PartialUser interface is equivalent to the following:
// interface PartialUser {
//     name?: string;
//     age?: number;
// }

Example #2

interface Todo {
  title: string;
  description: string;
}

function updateTodo(todo: Todo, fieldsToUpdate: Partial<Todo>) {
  return { ...todo, ...fieldsToUpdate };
}

const todo1 = {
  title: 'organize desk',
  description: 'clear clutter',
};

const todo2 = updateTodo(todo1, {
  description: 'throw out trash',
});

Example #3

interface Book {
  title: string;
  description: string;
  price: number;
}

interface IBookApiService {
  create(book: Book): Promise<string>;
  update(bookId: string, updates: Partial<Book>): Promise<void>;
  getBookById(bookId: string): Promise<Book | null>;
}

class BookApiService implements IBookApiService {
  async create(book: Book): Promise<string> {
    // Implementation will create book.
  }

  async update(bookId: string, updates: Partial<Book>): Promise<void> {
    // Implementation will update the book with the given ID.
  }

  async getBookById(bookId: string): Promise<Book | null> {
    // Implementation will return a book or null if not found.
  }
}