How can I specify a typed object literal in TypeScript?

Issue

Is there a way to make a typed object literal directly?

By directly I mean without having to assign it to a variable which is type annotated.

For example, I know I can do it like this:

export interface BaseInfo { value: number; }

export interface MyInfo extends BaseInfo { name: string; }

function testA(): BaseInfo = {
   const result: MyInfo = { value: 1, name: 'Hey!' };
   return result;
}

I also can do it like this:

function testB(): BaseInfo = {
   return { value: 1, name: 'Hey!' };
}

But what I need is something like:

function testC(): BaseInfo = {
   return { value: 1, name: 'Hey!' }: MyInfo; // <--- doesn't work
}

Or like this:

function testD(): BaseInfo = {
   return MyInfo: { value: 1, name: 'Hey!' }; // <--- doesn't work
}

Solution

Answer is to use the identity function:

function to<T>(value: T): T { return value; }
const instance = to<MyInfo>({
    value: 1,
    name: 'Hey!',
});

there should be no performance impact for an unnecessary call the to function, it should be optimized away by the JIT compiler

Answered By - Trident D'Gao