Utility Types that extend other Interfaces

Issue

I know that I can use utility types in type script, e.g. Pick, to build other types. But let's say after I Pick some of the properties from an interface, I want that new type to extend another interface.

export interface ICreateRequestVo {
};


export interface IFoo {
  foo: string;
  bar: string;
};

export type FooRequestVo = Pick<IFoo, 'foo'>;

Now when I try to make FooRequestVo extends ICreateRequestVo, I get the following error:

export type FooRequestVo = Pick<IFoo, 'foo'> extends ICreateRequestVo;

TS1005: '?' expected.

Solution

You probably want a type intersection:

type FooRequestVo = Pick<IFoo, 'foo'> & ICreateRequestVo;

Regarding the error: TypeScript thinks you want to use a conditional type such as:

type TypeE = TypeA extends TypeB ? typeC : typeD

Answered By - Conaclos