If I have a type with all required properties, how can I define another type with the same properties where some of it's properties are still required but the rest are optional?
For example I want a new type derived from SomeType where prop1 and prop2 are required but the rest are optional:
interface SomeType {
prop1;
prop2;
prop3;
...
propn;
}
interface NewType {
prop1;
prop2;
prop3?;
...
propn?;
}
You can use combination of Partial and Pick to make all properties partial and then pick only some that are required:
interface SomeType {
prop1: string;
prop2: string;
prop3: string;
propn: string;
}
type OptionalExceptFor<T, TRequired extends keyof T> = Partial<T> & Pick<T, TRequired>
type NewType = OptionalExceptFor<SomeType, 'prop1' | 'prop2'>
let o : NewType = {
prop1: "",
prop2: ""
}
type RequiredExceptFor<T, TOptional extends keyof T> = Pick<T, Diff<keyof T, TOptional>> & Partial<T>; with type Diff<T, U> = T extends U ? never : T;
type OptionalExceptFor<T, TRequired extends keyof T> = Partial<T> & Required<Pick<T, TRequired>>;
type onlyOneRequired = Partial<Tag> & {id: string}
In the above type, all properties of Tag are optional instead of id which is required.
So you can use this method and specify the required properties.
For tetter performance, in addition to Titian's answer, you must do :
type OptionalExceptFor<T, TRequired extends keyof T = keyof T> = Partial<
Pick<T, Exclude<keyof T, TRequired>>
> &
Required<Pick<T, TRequired>>;
From this article:
We can derive the following type:
export type PartialPick<T, F extends keyof T> = Omit<T, F> & Partial<Pick<T, F>>;
F - the fields that should be made optional
T - the type
In your example:
type NewType = PartialPick<SomeType, 'prop3' | ... | 'propn'>
If you'd like to make some properties required instead of the partial use:
type RequiredPick<T, F extends keyof T> = Omit<T, F> & Required<Pick<T, F>>;
If NewType should be an interface and has additional fields besides the fields in SomeType, you can use extends from the type:
interface SomeType {
prop1;
prop2;
prop3;
prop4;
}
interface NewType extends PartialPick<SomeType, 'prop3' | 'prop4'> {
prop5;
}
Here is another way
export type ContactInfoFormInput = Pick<AccountDetails, 'email' | 'phone'> &
Pick<Profile, 'firstName' | 'lastName'> & {
dateCreated?: Profile['dateCreated'];
};
So in this example, email, phone, firstName, lastName are all required but dateCreated which also comes from the Profile base type is optional
