For fetchPet.ts

import { QueryFunction } from "@tanstack/react-query";
import { PetAPIResponse } from "./APIResponsesTypes";

const fetchPet: QueryFunction<PetAPIResponse, ["details", string]> = async ({
}) => { … }
  • QueryFunction is a nice type we can use to not have to type ourselves
  • This forces the return type to be a PetAPIResponse
  • This makes sure that our fetchPet is only used with the 'details' key and that the second part of the query key is a string (otherwise it could be unknown)

Next let's do fetchSearch.ts

import { QueryFunction } from "@tanstack/react-query";
import { PetAPIResponse } from "./APIResponsesTypes";

const fetchSearch: QueryFunction<
      location: string;
      animal: string;
      breed: string;
> = async function ({ queryKey }) { … }

Same thing. We refactored to an assignment of a function because it types more easily that way.

Next let's do fetchBreedList.ts. First we need to add a new API response type to our APIResponseTypes.ts

export interface BreedListAPIResponse {
  animal: Animal;
  breeds: string[];

Now go back to fetchBreedList.ts

import { QueryFunction } from "@tanstack/react-query";
import { BreedListAPIResponse, Animal } from "./APIResponsesTypes";

const fetchBreedList: QueryFunction<
  ["breeds", Animal]
> = async ({ queryKey }) => { … }

Here we're explicitly making sure our string key is an Animal type and therefore we cannot have an invalid string. A little extra type defense that's pretty cheap. I'm a fan!

🏁 Click here to see the state of the project up until now: typescript-3