Access Object property in Typescript-CodePudding

I have function written in typescript where i am passing the object and key as an input parameter and in function return i am expecting the object with key value pair:

const article = {
    id: 1,
    title: "TypeScript Explained",
    active: true,
    getSlug: () => 'typescript-explained',
};

type Pick<T, U extends keyof T> = { [K in U]: T[K] };

function pick<T,U extends keyof T>(obj:T,key:U):Pick<T,U>{
    return  {[key]: obj[key]}
}

pick(article,'title')

But on calling the function i am getting the error like Type '{ [x: string]: T[U]; }' is not assignable to type 'Pick<T, U>'.

Can someone help?

CodePudding user response：

Typescript infers that type of {[key]: obj[key]} is { [x: string]: T[U]; }.

Thats why it panics when you try to return it as Pick<T,U>

You can either let it infer return type:

 function pick<T, U extends keyof T>(obj: T, key: U) {
    return { [key]: obj[key] };
  }

then function returns { [x: string]: T[U]; }

or explicitly set type of {[key]: obj[key]} with as:

 function pick<T, U extends keyof T>(obj: T, key: U): Pick<T, U> {
    return { [key]: obj[key] } as Pick<T, U>;
  }

then function returns value of type

Pick<{
    id: number;
    title: string;
    active: boolean;
    getSlug: () => string;
}, "title">