Axios library in React Native - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

What is the output when fetching data with Axios in React Native?

Consider this React Native component using Axios to fetch user data on button press. What will be displayed after pressing the button?

React Native

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

export default function UserFetcher() {
  const [user, setUser] = useState(null);
  const fetchUser = () => {
    axios.get('https://jsonplaceholder.typicode.com/users/1')
      .then(response => setUser(response.data))
      .catch(() => setUser({ name: 'Error' }));
  };
  return (
    <View>
      <Button title="Fetch User" onPress={fetchUser} />
      <Text>{user ? user.name : 'No user loaded'}</Text>
    </View>
  );
}

A Initially blank, then shows 'Error' after button press

B Shows 'No user loaded' always, button press does nothing

C Initially shows 'No user loaded', then after button press shows 'Leanne Graham'

D Shows 'No user loaded' initially, then blank after button press

💡 Hint

Think about what the Axios call returns and how state updates the displayed text.

The component starts with user as null, so it shows 'No user loaded'. When the button is pressed, Axios fetches user data and sets user to the response. The user name 'Leanne Graham' is then displayed.

❓ lifecycle

intermediate

When does Axios fetch data in this React Native component?

Given this component, when is the Axios GET request triggered?

React Native

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

export default function DataLoader() {
  const [data, setData] = useState(null);
  useEffect(() => {
    axios.get('https://jsonplaceholder.typicode.com/posts/1')
      .then(response => setData(response.data))
      .catch(() => setData({ title: 'Error' }));
  }, []);
  return <View><Text>{data ? data.title : 'Loading...'}</Text></View>;
}

A When the component unmounts

B Only once when the component first mounts

C Every time the component re-renders

D When the user presses a button

💡 Hint

Look at the dependency array in useEffect.

The empty dependency array [] means the effect runs only once after the component mounts, triggering the Axios GET request once.

📝 Syntax

advanced

Which Axios call correctly sends JSON data in a POST request?

Choose the correct Axios POST request syntax to send JSON data { name: 'John' } to the endpoint.

A axios.post('https://api.example.com/users', { name: 'John' })

B axios.post('https://api.example.com/users', JSON.stringify({ name: 'John' }))

C axios.post('https://api.example.com/users', { name: 'John' }, { headers: { 'Content-Type': 'text/plain' } })

D axios.post('https://api.example.com/users', null, { data: { name: 'John' } })

💡 Hint

Axios automatically sets the correct headers and stringifies the data object.

Option A correctly passes the data object directly. Axios sets the Content-Type to application/json and stringifies the object automatically. Option A sends a string but Axios expects an object. Option A sets wrong headers. Option A misuses the config object.

🔧 Debug

advanced

Why does this Axios request cause a runtime error?

Examine this code snippet. What causes the runtime error?

React Native

import axios from 'axios';

async function fetchData() {
  try {
    const response = await axios.get('https://api.example.com/data');
    console.log(response.data);
  } catch (error) {
    console.log(error.message);
  }
}

fetchData();

A The function fetchData is not awaited or handled properly

B Missing import of React in the file

C axios.get URL is missing protocol

D Using await outside an async function

💡 Hint

Look at how fetchData is called.

The function fetchData is async but called without awaiting or handling its promise. This can cause unhandled promise rejections or unexpected behavior. The code itself is valid but best practice is to await or handle the promise.

🧠 Conceptual

expert

What is the effect of setting Axios interceptors in React Native?

Which statement best describes the purpose of Axios interceptors in a React Native app?

A They convert all Axios calls to fetch API calls internally

B They automatically retry failed requests without any code

C They cache all responses locally to improve performance

D They allow modifying requests or responses globally before they are handled by then or catch

💡 Hint

Think about how interceptors can change requests or responses.

Axios interceptors let you add code to run before a request is sent or before a response is handled. This is useful for adding headers, logging, or error handling globally. They do not automatically retry, cache, or convert calls.