Fetch API for GET requests in React Native - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

What will this React Native component display after fetching data?

Consider this React Native component that fetches user data from an API and displays the user's name. What will be shown on the screen after the fetch completes successfully?

React Native

import React, { useState, useEffect } from 'react';
import { Text, View } from 'react-native';

export default function UserName() {
  const [name, setName] = useState('Loading...');

  useEffect(() => {
    fetch('https://api.example.com/user/1')
      .then(response => response.json())
      .then(data => setName(data.name))
      .catch(() => setName('Error'));
  }, []);

  return (
    <View>
      <Text>{name}</Text>
    </View>
  );
}

A Displays 'Loading...' forever because useEffect is missing dependencies.

B Displays the user's name fetched from the API, e.g., 'Alice'.

C Displays 'Error' because fetch is not awaited.

D Displays nothing because the component returns null.

💡 Hint

Think about what happens after the fetch promise resolves and how state updates affect rendering.

The component starts with 'Loading...'. After fetch completes, it updates the state with the user's name, causing the component to re-render and display the name.

📝 Syntax

intermediate

Which fetch call syntax correctly performs a GET request?

You want to fetch data from 'https://api.example.com/items' using fetch in React Native. Which option correctly performs a GET request?

A fetch('https://api.example.com/items', { body: '{}' })

B fetch('https://api.example.com/items', { method: 'POST' })

C fetch('https://api.example.com/items', { method: 'GET' })

D fetch('https://api.example.com/items', { headers: { 'Content-Type': 'application/json' } })

💡 Hint

GET is the default method for fetch, but specifying it explicitly is correct.

Option C explicitly sets method to 'GET', which is correct. Option C uses POST, which is wrong. Option C adds a body, which is invalid for GET. Option C sets headers but does not specify method, so it defaults to GET but is incomplete for this question.

❓ lifecycle

advanced

When does the fetch call inside useEffect run in this React Native component?

Given this component, when will the fetch call execute?

React Native

import React, { useEffect } from 'react';
import { Text } from 'react-native';

export default function DataFetcher() {
  useEffect(() => {
    fetch('https://api.example.com/data')
      .then(res => res.json())
      .then(console.log);
  }, []);

  return <Text>Fetching data...</Text>;
}

A Only once, right after the component mounts.

B Every time the component re-renders.

C Only when the component unmounts.

D Every time the user taps the screen.

💡 Hint

Look at the dependency array in useEffect.

An empty dependency array means the effect runs only once after the component mounts.

🔧 Debug

advanced

What error does this fetch code produce?

This React Native code tries to fetch JSON data but has a bug. What error will it cause?

React Native

fetch('https://api.example.com/data')
  .then(response => response.json)
  .then(data => console.log(data));

A ReferenceError: data is not defined

B SyntaxError: Unexpected token in JSON

C TypeError: response.json is not a function

D No error, logs the response.json function reference instead of the data

💡 Hint

Check how response.json is called.

response.json is a function and must be called with parentheses. Without (), it returns a reference to the function itself (not a promise from calling it), so the next .then receives the function and logs it. No error is thrown.

🧠 Conceptual

expert

Why should you handle errors when using fetch for GET requests in React Native?

Which is the best reason to handle errors when fetching data with fetch in React Native?

A Because network requests can fail due to no internet or server issues, and the app should respond gracefully.

B Because fetch automatically retries failed requests unless errors are handled.

C Because fetch throws a syntax error if the URL is a string.

D Because handling errors makes the fetch call faster.

💡 Hint

Think about real-life situations like losing internet connection.

Network requests can fail for many reasons. Handling errors lets the app show messages or fallback UI instead of crashing or freezing.

Practice

1.

What does the Fetch API do in React Native?

Choose the best description.

easy

A. It retrieves data from a web server using HTTP requests.

B. It styles components with CSS.

C. It manages app navigation between screens.

D. It stores data locally on the device.

Solution

1. Step 1: Understand Fetch API purpose

   The Fetch API is designed to make network requests to get or send data.

2. Step 2: Match description to Fetch API

   Only It retrieves data from a web server using HTTP requests. describes retrieving data from a web server, which is what Fetch does.

3. Final Answer:

   It retrieves data from a web server using HTTP requests. -> Option A

4. Quick Check:

   Fetch API = Data retrieval [OK]

Hint: Fetch is for network data requests, not styling or storage [OK]

Common Mistakes:

• Confusing Fetch with styling or navigation libraries
• Thinking Fetch stores data locally
• Assuming Fetch only works with JSON

2.

Which of the following is the correct syntax to fetch JSON data from https://api.example.com/data?

fetch(_____).then(response => response.json())

easy

A. "https://api.example.com/data"

B. url

C. https://api.example.com/data

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

Solution

1. Step 1: Identify correct string syntax in JavaScript

   URLs must be passed as strings, enclosed in quotes.

2. Step 2: Choose proper quotes for URL string

   'https://api.example.com/data' uses single quotes correctly.

3. Final Answer:

   'https://api.example.com/data' -> Option D

4. Quick Check:

   URL as string = 'https://api.example.com/data' [OK]

Hint: Always wrap URLs in quotes for fetch [OK]

Common Mistakes:

• Not using quotes around the URL
• Using undefined variable url without declaration
• Using double quotes inside double quotes without escaping

3.

What will be logged to the console after running this code?

fetch('https://api.example.com/user')
  .then(response => response.json())
  .then(data => console.log(data.name))
  .catch(error => console.error(error));

Assume the server returns { "name": "Alice" }.

medium

A. SyntaxError

B. undefined

C. Alice

D. null

Solution

1. Step 1: Understand fetch and JSON parsing

   The fetch call gets the response, then response.json() parses it into an object.

2. Step 2: Access the 'name' property from parsed data

   The data object has a 'name' key with value "Alice", so console.log(data.name) prints "Alice".

3. Final Answer:

   Alice -> Option C

4. Quick Check:

   Parsed JSON name = Alice [OK]

Hint: Parsed JSON data properties print their values [OK]

Common Mistakes:

• Logging before JSON parsing
• Trying to access data.name before fetch resolves
• Ignoring asynchronous nature of fetch

4.

Identify the error in this fetch code snippet:

fetch('https://api.example.com/items')
  .then(response => response.json)
  .then(data => console.log(data))
  .catch(error => console.error(error));

medium

A. Missing parentheses after response.json() call

B. URL string is not quoted properly

C. No catch block to handle errors

D. Using console.log instead of alert

Solution

1. Step 1: Check response.json usage

   response.json is a function and must be called with parentheses to parse JSON.

2. Step 2: Identify missing parentheses error

   The code uses response.json without () which returns the function itself, not the parsed data.

3. Final Answer:

   Missing parentheses after response.json() call -> Option A

4. Quick Check:

   Call response.json() with () [OK]

Hint: Always call response.json() with parentheses [OK]

Common Mistakes:

• Forgetting parentheses on response.json
• Misplacing catch block
• Using wrong quotes for URL

5.

You want to fetch user data and show a loading message while waiting. Which code snippet correctly handles loading state and errors?

const [loading, setLoading] = React.useState(true);
const [error, setError] = React.useState(null);

React.useEffect(() => {
  fetch('https://api.example.com/user')
    .then(res => res.json())
    .then(data => {
      // handle data
      setLoading(false);
    })
    .catch(err => {
      setError(err.message);
      setLoading(false);
    });
}, []);

What is missing to properly show loading and error states?

hard

A. Remove catch block to avoid errors

B. Render UI that shows loading and error messages based on state

C. Call setLoading(true) inside fetch then block

D. Use async/await instead of then/catch

Solution

1. Step 1: Understand state variables usage

   loading and error states are set correctly during fetch lifecycle.

2. Step 2: Identify missing UI rendering logic

   Without UI code that checks loading and error states, user won't see messages.

3. Final Answer:

   Render UI that shows loading and error messages based on state -> Option B

4. Quick Check:

   Show loading/error UI based on state [OK]

Hint: Set state is not enough; render UI accordingly [OK]

Common Mistakes:

• Not rendering loading or error messages
• Setting loading true too late
• Ignoring error handling in UI