Typescript - How to return dynamic "object key" that comes from dynamic "prop key value"?

user_1388541 0
Viewed 963

I'm trying to generate "dynamic object key" based of "prop key value" by picking specific object key value.

So let's say I pass in { name: 'someEntity', unrelatedKey: 123 } and I would like to return { someEntity: 'ok' }. How would one do that so the return value is typescript type defined? I've tried something like this but it does not work:

type GetExampleProps = {
  name: string
  unrelatedKey: number
}

type GetExampleRes<T> = {
  [key: T]: string
}

function getExample<T extends GetExampleProps> (props: T): GetExampleRes<T['name']> {
  return {
    [props.name]: 'ok'
  }
}

const example = getExample({ name: 'someEntity', unrelatedKey: 123 })

example.someEntity  // should be valid type string
example.hello       // should be invalid, missing key
typescript-generics typescript javascript
2 Answers

Currently I am unable to do that without a type assertion, but as a temporary solution here it is:

type GetExampleProps<T extends PropertyKey = string> = {
  name: T;
  unrelatedKey: number;
};

function getExample<T extends PropertyKey>(
  props: GetExampleProps<T>
): {
  [K in T]: string;
} {
  const toRet = {
    [props.name]: "a string",
  };

  return toRet as { [K in T]: string };
}

const example = getExample({ name: "someEntity", unrelatedKey: 123 });

example.someEntity;
example.hello; // Property 'hello' does not exist on type '{ someEntity: string; }'
user_81377540

Try this function, this should work the way you need

const createObject = (obj: any) => {
    interface I {
        [name: string]: any;
    }
    const returnObj: I = {};
    returnObj[obj.name] = Object.keys(obj).filter((key) => key !== "name");
    return returnObj;
};
user_87974130
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