Make a single property optional in TypeScript

Question

In TypeScript, 2.2...

Let's say I have a Person type:

interface Person {   name: string;   hometown: string;   nickname: string; } 

And I'd like to create a function that returns a Person, but doesn't require a nickname:

function makePerson(input: ???): Person {   return {...input, nickname: input.nickname || input.name}; } 

What should be the type of input? I'm looking for a dynamic way to specify a type that is identical to Person except that nickname is optional (nickname?: string | undefined). The closest thing I've figured out so far is this:

type MakePersonInput = Partial<Person> & {   name: string;   hometown: string; } 

but that's not quite what I'm looking for, since I have to specify all the types that are required instead of the ones that are optional.

Answer 1

You can also do something like this, partial only some of the keys.

type Omit<T, K extends keyof T> = Pick<T, Exclude<keyof T, K>> type PartialBy<T, K extends keyof T> = Omit<T, K> & Partial<Pick<T, K>>  interface Person {   name: string;   hometown: string;   nickname: string; }  type MakePersonInput = PartialBy<Person, 'nickname'>