Posted on Sep 21, 2023

Day 53: Deep Readonly

Question

Create a type that makes all properties of a deeply nested object readonly, you can use TypeScript's recursive conditional types. Here's an example of how to define such a type.

type DeepReadonly<T> = // Todo add your code here // Example usage interface Person { name: string; age: number; address: { street: string; city: string; }; } type ReadonlyPerson = DeepReadonly<Person>; const person: ReadonlyPerson = { name: 'John', age: 30, address: { street: '123 Main St', city: 'Exampleville', }, }; // This will result in a TypeScript error because properties are readonly: // person.name = 'Alice'; // person.address.street = '456 Elm St';

Top comments (1)

Dharan Ganesan • Sep 21 '23

type DeepReadonly<T> = { readonly [K in keyof T]: T[K] extends object ? DeepReadonly<T[K]> : T[K]; }; // Example usage interface Person { name: string; age: number; address: { street: string; city: string; }; } const person: DeepReadonly<Person> = { name: 'John', age: 30, address: { street: '123 Main St', city: 'Exampleville', }, }; // person.name = 'Alice'; // person.address.street = '456 Elm St';