React Intermediate Part 2 - Fetching Data

I think to be following religiously the course material, but I am getting two errors in the below TodoList.tsx file that has me blocked. I thank you in advance for your help.

Error 1 on line 18: queryKey: [“todos”],
The error is:
No overload matches this call.
The last overload gave the following error.
Argument of type ‘{ queryKey: string[]; queryFn: () => () => Promise<Todo[]>; }’ is not assignable to parameter of type ‘QueryKey’.
Object literal may only specify known properties, and ‘queryKey’ does not exist in type ‘readonly unknown[]’.ts(2769)
useQuery.d.ts(16, 25): The last overload is declared here.

Error 2 on line 26: {todos?.map((todo) => (
The error is:
Property ‘map’ does not exist on type ‘NonNullable’.

import { useQuery } from "@tanstack/react-query";
import axios from "axios";

interface Todo {
    id: number;
    title: string;
    userId: number;
    completed: boolean;

const TodoList = () => {
    const fetchTodos = () =>
            .then((res) =>;

    const { data: todos, error } = useQuery<Todo[], Error>({
        queryKey: ["todos"],
        queryFn: () => fetchTodos,

    if (error) return <p>{error.message}</p>;

    return (
        <ul className="list-group">
            {todos?.map((todo) => (
                <li key={} className="list-group-item">

export default TodoList;

Started the course this morning and got the exact same error. :crossed_fingers: Hopefully someone has a solution for this.

So I found the problem in the code…you have to remove the arrow function from the queryFn - like below:

const { data: todos, error } = useQuery<Todo[], Error>({
        queryKey: ["todos"],
        queryFn: fetchTodos,

Mine is working now… Hope this helps.

Checkout the docs on tanstack regarding useQuery: Queries | TanStack Query Docs

1 Like

Thank you, it works! :tada: It is now perfectly clear why the error was happening. This happens sometimes when studying late at night.

Happens to me all the time. I find using difchecker very helpful:

For anyone else receiving this error, if you have added curly braces to your fetchTodos function, remember to return the axios methods in the function body as you won’t have an implicit return from the concise body arrow function. This caught me out, and I received the same error listed above.