AsyncStorage for key-value in React Native - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

What is the output when saving and retrieving a value with AsyncStorage?

Consider this React Native code snippet using AsyncStorage. What will be displayed in the Text component after pressing the button?

React Native

import React, { useState } from 'react';
import { View, Text, Button } from 'react-native';
import AsyncStorage from '@react-native-async-storage/async-storage';

export default function App() {
  const [storedValue, setStoredValue] = useState('');

  const saveValue = async () => {
    await AsyncStorage.setItem('greeting', 'Hello!');
    const value = await AsyncStorage.getItem('greeting');
    setStoredValue(value || '');
  };

  return (
    <View>
      <Button title="Save and Load" onPress={saveValue} />
      <Text>{storedValue}</Text>
    </View>
  );
}

A The Text component shows: undefined

B The Text component shows: Hello!

C The Text component shows: null

D The Text component remains empty

💡 Hint

Remember AsyncStorage stores strings and getItem returns the stored string or null if not found.

The code saves the string 'Hello!' under the key 'greeting'. Then it retrieves it immediately and sets it to state. So the Text component displays 'Hello!'.

❓ lifecycle

intermediate

When should you load AsyncStorage data in a React Native component?

You want to load a saved username from AsyncStorage when your screen appears. Which React hook is best to use for this?

A useEffect with no dependency array

B useState to load data directly

C useMemo to load data once

D useEffect with an empty dependency array []

💡 Hint

Think about running code once when the component mounts.

useEffect with [] runs once when the component mounts, perfect for loading data from AsyncStorage once on screen load.

🔧 Debug

advanced

What error does this AsyncStorage code produce?

Look at this code snippet. What error will it cause when run?

React Native

import AsyncStorage from '@react-native-async-storage/async-storage';

async function getData() {
  const value = await AsyncStorage.getItem('key');
  console.log(value);
}

getData();

A It logs a Promise object instead of the stored value

B SyntaxError due to missing await keyword

C TypeError because getItem is not a function

D It logs null if the key does not exist

💡 Hint

Remember AsyncStorage.getItem returns a Promise.

Without await, value is a Promise object, so console.log prints the Promise, not the resolved string.

🧠 Conceptual

advanced

How does AsyncStorage handle data types?

Which statement about AsyncStorage data storage is true?

A AsyncStorage stores only strings; other types must be converted before saving

B AsyncStorage stores data in binary format for efficiency

C AsyncStorage automatically serializes objects and arrays

D AsyncStorage supports storing numbers directly without conversion

💡 Hint

Think about what happens if you try to save an object directly.

AsyncStorage stores only strings. To save objects or arrays, you must convert them to strings (e.g., JSON.stringify) before saving.

❓ navigation

expert

What happens if you navigate away before AsyncStorage.setItem completes?

In a React Native app, you call AsyncStorage.setItem to save data, then immediately navigate to another screen. What is the likely outcome?

A Navigation waits automatically until setItem finishes saving

B The data is always saved instantly before navigation happens

C The data may not be saved because setItem is asynchronous and might be interrupted

D An error is thrown if navigation happens before setItem completes

💡 Hint

AsyncStorage operations are asynchronous and do not block navigation.

AsyncStorage.setItem is asynchronous and does not block navigation. If you navigate away immediately, the save might not complete before the app state changes.

Practice

1. What is the main purpose of AsyncStorage in React Native?

easy

A. To create complex animations in the app

B. To handle network requests and API calls

C. To store small amounts of data as key-value pairs on the device

D. To manage app navigation between screens

Solution

1. Step 1: Understand AsyncStorage's role

   AsyncStorage is designed to save simple data like user preferences as key-value pairs on the device.

2. Step 2: Compare with other options

   Animations, network requests, and navigation are handled by other libraries or APIs, not AsyncStorage.

3. Final Answer:

   To store small amounts of data as key-value pairs on the device -> Option C

4. Quick Check:

   AsyncStorage = key-value storage [OK]

Hint: AsyncStorage saves simple data locally as key-value pairs [OK]

Common Mistakes:

• Confusing AsyncStorage with network or UI libraries
• Thinking AsyncStorage manages navigation or animations

2. Which of the following is the correct way to save a value using AsyncStorage in React Native?

easy

A. await AsyncStorage.setItem('key', 'value');

B. AsyncStorage.save('key', 'value');

C. AsyncStorage.store('key', 'value');

D. await AsyncStorage.put('key', 'value');

Solution

1. Step 1: Recall AsyncStorage method for saving data

   The correct method to save data is setItem, which returns a promise and requires await.

2. Step 2: Check method names

   Methods like save, store, and put do not exist in AsyncStorage API.

3. Final Answer:

   await AsyncStorage.setItem('key', 'value'); -> Option A

4. Quick Check:

   Save data = setItem [OK]

Hint: Use setItem with await to save data [OK]

Common Mistakes:

• Using incorrect method names like save or put
• Forgetting to use await with async calls

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

import AsyncStorage from '@react-native-async-storage/async-storage';

async function test() {
  await AsyncStorage.setItem('name', 'Alice');
  const value = await AsyncStorage.getItem('name');
  console.log(value);
}
test();

medium

A. Alice

B. null

C. Error: AsyncStorage not found

D. undefined

Solution

1. Step 1: Analyze setItem and getItem usage

   The code saves the string 'Alice' under the key 'name' and then retrieves it correctly using await.

2. Step 2: Understand console output

   Since the value was saved and retrieved successfully, console.log prints 'Alice'.

3. Final Answer:

   Alice -> Option A

4. Quick Check:

   Saved value retrieved = Alice [OK]

Hint: getItem returns saved string or null if missing [OK]

Common Mistakes:

• Expecting undefined instead of null or string
• Not awaiting async calls causing errors

4. Identify the error in this AsyncStorage usage:

import AsyncStorage from '@react-native-async-storage/async-storage';

function saveData() {
  AsyncStorage.setItem('token', 'abc123');
  console.log('Token saved');
}
saveData();

medium

A. console.log should be inside a .then() callback

B. Wrong method name setItem should be saveItem

C. AsyncStorage must be imported from 'react-native' not '@react-native-async-storage/async-storage'

D. Missing await before AsyncStorage.setItem causing unhandled promise

Solution

1. Step 1: Check async usage of setItem

   AsyncStorage.setItem returns a promise and should be awaited or handled with then to ensure completion.

2. Step 2: Identify missing await

   The function saveData is not async and does not await setItem, so the promise is unhandled and may cause issues.

3. Final Answer:

   Missing await before AsyncStorage.setItem causing unhandled promise -> Option D

4. Quick Check:

   AsyncStorage.setItem needs await [OK]

Hint: Always await AsyncStorage async calls to avoid unhandled promises [OK]

Common Mistakes:

• Forgetting to make function async and use await
• Using wrong import source
• Incorrect method names

5. You want to remove a saved user preference with key 'theme' and then confirm it is removed. Which code snippet correctly does this?

hard

A. await AsyncStorage.clear('theme'); const val = await AsyncStorage.getItem('theme'); console.log(val);

B. await AsyncStorage.removeItem('theme'); const val = await AsyncStorage.getItem('theme'); console.log(val);

C. AsyncStorage.delete('theme'); const val = AsyncStorage.get('theme'); console.log(val);

D. AsyncStorage.remove('theme'); const val = AsyncStorage.getItem('theme'); console.log(val);

Solution

1. Step 1: Identify correct method to remove a key

   The correct method to remove a key is removeItem, which returns a promise and should be awaited.

2. Step 2: Confirm removal by getting the key

   After removal, calling getItem returns null, confirming deletion.

3. Final Answer:

   await AsyncStorage.removeItem('theme'); const val = await AsyncStorage.getItem('theme'); console.log(val); -> Option B

4. Quick Check:

   Remove key = removeItem + await [OK]

Hint: Use removeItem with await to delete keys safely [OK]

Common Mistakes:

• Using non-existent methods like delete or remove
• Not awaiting async calls
• Using clear which removes all keys, not one