Allow Typescript to understand which keys on an object were passed into function

I’m not sure this is possible so any ideas would be appreciated. Rather than trying to explain it I think the easiest way is with an example..

interface Queries {
    foo?: string;
    boo?: string;
    bar?: string;
}

const go = async (arg1: Queries): DynamicReturnType => {
    // Is it possible in the return type of the function to only specify the keys that were passed in ie: { foo: string; bar: string })
   return arg1;
}

const result = go({
    foo: "fooooo",
    bar: "baaaaarr"
}); // Ideally the type for 'result' would be { foo: string; bar: string; }

>Solution :

Looks like you want go() to be generic in the type of its argument. So arg1 should not be of specific type Queries, but of some generic type T constrained to Queries. Like this:

const go = <T extends Queries>(arg1: T): T => {    
    return arg1;
}

And that gives you the desired behavior:

const result = go({
    foo: "fooooo",
    bar: "baaaaarr"
});
/* const result: {
    foo: string;
    bar: string;
} */

Playground link to code