React Query for data fetching in React Native - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the main hook from React Query.

React Native

import { [1] } from '@tanstack/react-query';

Drag options to blanks, or click blank then click option'

AuseState

BuseContext

CuseQuery

DuseEffect

Attempts:

3 left

💡 Hint

Common Mistakes

Using React built-in hooks like useState or useEffect instead of useQuery.

Trying to import useContext which is unrelated to data fetching.

The useQuery hook is the main React Query hook used to fetch data.

2fill in blank

medium

Complete the code to fetch data from the API endpoint using useQuery.

React Native

const { data, isLoading } = useQuery(['todos'], () => fetch('[1]').then(res => res.json()));

Drag options to blanks, or click blank then click option'

A'https://api.example.com/todos'

B'/local/data.json'

C'https://wrong.url/api'

D'http://localhost:3000'

Attempts:

3 left

💡 Hint

Common Mistakes

Using a local file path instead of an API URL.

Using an incorrect or unreachable URL.

The URL 'https://api.example.com/todos' is the correct API endpoint to fetch todos.

3fill in blank

hard

Fix the error in the code by completing the missing option to enable refetching on window focus.

React Native

const { data, refetch } = useQuery(['user'], fetchUser, { refetchOnWindow[1]: true });

Drag options to blanks, or click blank then click option'

ABlur

BLoad

CClick

DFocus

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'refetchOnWindowBlur' which is not a valid option.

Using unrelated words like 'Click' or 'Load'.

The option refetchOnWindowFocus enables React Query to refetch data when the window gains focus.

4fill in blank

hard

Fill both blanks to create a query key and a fetch function for React Query.

React Native

const { data } = useQuery([[1]], () => fetch([2]).then(res => res.json()));

Drag options to blanks, or click blank then click option'

A'posts'

B'https://api.example.com/posts'

C'users'

D'https://api.example.com/users'

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing query keys and URLs incorrectly.

Using mismatched keys and URLs.

The query key 'posts' matches the API endpoint 'https://api.example.com/posts' to fetch posts data.

5fill in blank

hard

Fill all three blanks to destructure data, loading state, and error from useQuery.

React Native

const { [1], [2], [3] } = useQuery(['profile'], fetchProfile);

Drag options to blanks, or click blank then click option'

Adata

BisLoading

Cerror

DsetData

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to destructure setter functions like setData which React Query does not provide.

Missing one of the three important properties.

React Query returns data, isLoading, and error to handle fetched data, loading state, and errors.

Practice

1. What is the main purpose of using useQuery in React Query for React Native apps?

easy

A. To style components dynamically

B. To fetch and manage server data easily with caching and updates

C. To navigate between screens

D. To handle local state only

Solution

1. Step 1: Understand the role of useQuery

   useQuery is designed to fetch data from a server and manage it efficiently in React apps.

2. Step 2: Identify its features

   It automatically handles loading states, errors, caching, and data updates, making server data management easier.

3. Final Answer:

   To fetch and manage server data easily with caching and updates -> Option B

4. Quick Check:

   useQuery purpose = fetch and manage data [OK]

Hint: Remember: useQuery is for fetching and caching data [OK]

Common Mistakes:

• Confusing useQuery with navigation or styling hooks
• Thinking useQuery manages only local state
• Assuming useQuery is for UI rendering only

2. Which of the following is the correct syntax to use useQuery to fetch data with a key 'todos' and a fetch function fetchTodos?

easy

A. const { data } = useQuery('todos', fetchTodos);

B. const data = useQuery(fetchTodos, 'todos');

C. useQuery(fetchTodos, { key: 'todos' });

D. const { data } = useQuery({ key: 'todos', fetch: fetchTodos });

Solution

1. Step 1: Recall the useQuery syntax

   The correct syntax is useQuery(key, fetchFunction), where the first argument is a unique key and the second is the function to fetch data.

2. Step 2: Match the options

   const { data } = useQuery('todos', fetchTodos); matches this syntax exactly: useQuery('todos', fetchTodos).

3. Final Answer:

   const { data } = useQuery('todos', fetchTodos); -> Option A

4. Quick Check:

   useQuery(key, fetchFn) = const { data } = useQuery('todos', fetchTodos); [OK]

Hint: useQuery takes key first, then fetch function [OK]

Common Mistakes:

• Swapping the order of arguments
• Passing an object instead of separate arguments
• Not destructuring the returned data

3. Given this code snippet:

const fetchUser = async () => {
  return { name: 'Alice', age: 30 };
};

const { data, isLoading, error } = useQuery('user', fetchUser);

if (isLoading) return <Text>Loading...</Text>;
if (error) return <Text>Error!</Text>;

return <Text>{data.name} is {data.age} years old.</Text>;

What will be displayed after the data loads successfully?

medium

A. Loading...

B. Error!

C. Alice is 30 years old.

D. undefined is undefined years old.

Solution

1. Step 1: Analyze the fetch function and query

   The fetchUser function returns an object with name 'Alice' and age 30. useQuery fetches this data with key 'user'.

2. Step 2: Understand the rendering logic

   While loading, it shows 'Loading...'. On error, it shows 'Error!'. After successful fetch, it renders the text with data values.

3. Final Answer:

   Alice is 30 years old. -> Option C

4. Quick Check:

   Data loaded = Alice is 30 years old [OK]

Hint: Check loading and error before rendering data [OK]

Common Mistakes:

• Ignoring loading or error states
• Accessing data before it loads
• Assuming data is undefined

4. Identify the error in this React Query usage:

const { data, isLoading } = useQuery(fetchPosts, 'posts');

medium

A. The arguments to useQuery are reversed; key should come first

B. useQuery requires a third argument for options

C. Destructuring data and isLoading is not allowed

D. fetchPosts should be a string, not a function

Solution

1. Step 1: Check the argument order for useQuery

   The correct order is useQuery(key, fetchFunction). Here, the fetch function is passed first, then the key.

2. Step 2: Identify the mistake

   The arguments are reversed, which will cause an error or unexpected behavior.

3. Final Answer:

   The arguments to useQuery are reversed; key should come first -> Option A

4. Quick Check:

   useQuery(key, fetchFn) order matters [OK]

Hint: Key always comes before fetch function in useQuery [OK]

Common Mistakes:

• Swapping key and fetch function arguments
• Forgetting to pass a unique key
• Assuming fetch function can be a string

5. You want to fetch a list of posts and automatically refetch the data every 10 seconds using React Query. Which code snippet correctly implements this behavior?

hard

A. const { data } = useQuery('posts', fetchPosts, { staleTime: 10000 });

B. const { data } = useQuery('posts', fetchPosts, { refetchOnWindowFocus: true });

C. const { data } = useQuery('posts', fetchPosts, { cacheTime: 10000 });

D. const { data } = useQuery('posts', fetchPosts, { refetchInterval: 10000 });

Solution

1. Step 1: Understand refetching options in React Query

   To refetch data automatically at intervals, use the refetchInterval option with the interval time in milliseconds.

2. Step 2: Match the correct option

   const { data } = useQuery('posts', fetchPosts, { refetchInterval: 10000 }); uses refetchInterval: 10000 which means refetch every 10 seconds. Other options control different behaviors.

3. Final Answer:

   const { data } = useQuery('posts', fetchPosts, { refetchInterval: 10000 }); -> Option D

4. Quick Check:

   Auto refetch = refetchInterval option [OK]

Hint: Use refetchInterval to auto-refresh data periodically [OK]

Common Mistakes:

• Confusing refetchOnWindowFocus with interval refetch
• Using cacheTime or staleTime incorrectly
• Not passing options as third argument