Make the TypeScript interface partially optional/required
I came across a situation when I had to make a single key of the TypeScript interface optional. Let’s say that I have a type that consists of two keys, name and age, and I want to make the age key optional. My real-life scenario was more convoluted, but I just want to show you what I learned. Look!
interface Dude {
name: string;
age: number;
}
// 👍 OK, name and age are defined
const pawel: Dude = {
name: "Pawel Grzybek",
age: 34,
};
// 👎 Uuups, age is missing
const dan: Dude = {
name: "Dan Jordan",
};
TypeScript comes with two handy utility types. The Partial converts all keys to optional and Required that makes all keys mandatory.
interface Dude {
name: string;
age: number;
}
type DudeAllOptional = Partial<Dude>;
// 👍 OK, name and age are optional
const dan: DudeAllOptional = {};
interface Dude {
name: string;
age?: number;
}
type DudeAllRequired = Required<Dude>;
// 👎 Uuups, age is missing
const dan: DudeAllRequired = {
name: "Dan Jordan",
};
These two utility types are super helpful, but it didn’t solve my problem to make only a subset of keys optional. So I took a moment to brainstorm this idea with my friend Matias (hi dude 👋), and we came up with this solution.
interface Dude {
name: string;
age: number;
}
type DudeWithOptionalAge = Omit<Dude, "age"> & Partial<Pick<Dude, "age">>;
// 👍 name is defined, age is optional
const dan: DudeWithOptionalAge = {
name: "Dan Jordan",
};
Problem solved, but we can do better. This type looks ridiculous, and without a good coffee, I don’t want to make any edits to it. But, thanks to generics, we can wrap it in a little utility type and reuse it all over the place.
type PartiallyOptional<T, K extends keyof T> = Omit<T, K> & Partial<Pick<T, K>>;
interface Dude {
name: string;
age: number;
}
type DudeWithOptionalAge = PartiallyOptional<Dude, "age">;
// 👍 name is defined, age is optional
const dan: DudeWithOptionalAge = {
name: "Dan Jordan",
};
type PartiallyRequired<T, K extends keyof T> = Omit<T, K> & Required<Pick<T, K>>;
interface Dude {
name: string;
age?: number;
}
type DudeWithRequiredAge = PartiallyRequired<Dude, "age">;
// 👎 Uuups, age is missing
const dan: DudeWithRequiredAge = {
name: "Dan Jordan",
};
If you know a better solution to my problem then please drop a comment below. If you don’t know a better way of doing it, I hope you learned a thing or two. Until next time, stay curious 🤩
hey bro! 👋 love pairing with you :D
If you like this kind of types you'll love fiddling with https://github.com/millsp/ts-toolbelt
Is the
Omitnecessary?