File system access in React Native - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the file system module in React Native.

React Native

import [1] from 'react-native-fs';

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

AFileSys

BRNFS

Cfs

DFileSystem

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'fs' which is a Node.js module, not React Native.

Using 'FileSystem' which is from Expo, not react-native-fs.

The common alias for the react-native-fs module is RNFS, which provides file system access.

2fill in blank

medium

Complete the code to read a file's content as a string.

React Native

RNFS.readFile([1], 'utf8').then(contents => {
  console.log(contents);
});

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

AfilePath

BfileUri

CfileName

DfileData

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the file name without path, which causes file not found error.

Using 'fileUri' which is not the expected parameter here.

The readFile function requires the file path as the first argument to read its contents.

3fill in blank

hard

Fix the error in the code to write text to a file.

React Native

RNFS.[1](filePath, 'Hello World').then(() => {
  console.log('File written');
});

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

Awrite

BwriteText

CwriteFile

DsaveFile

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'write' which does not exist in react-native-fs.

Using 'writeText' or 'saveFile' which are invalid method names.

The correct method to write text to a file in react-native-fs is writeFile.

4fill in blank

hard

Fill both blanks to check if a file exists and then delete it.

React Native

RNFS.[1](filePath).then(exists => {
  if (exists) {
    RNFS.[2](filePath).then(() => console.log('Deleted'));
  }
});

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

Aexists

BfileExists

Cunlink

DdeleteFile

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'fileExists' which is not a method in react-native-fs.

Using 'deleteFile' which is not the correct method name.

The method to check if a file exists is 'exists', and to delete a file is 'unlink' in react-native-fs.

5fill in blank

hard

Fill all three blanks to create a directory, write a file inside it, and then read the file.

React Native

RNFS.[1](dirPath).then(() => {
  return RNFS.[2](filePath, 'Sample Text');
}).then(() => {
  return RNFS.[3](filePath, 'utf8');
}).then(contents => {
  console.log(contents);
});

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

Amkdir

BwriteFile

CreadFile

DcreateDir

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'createDir' which is not a method in react-native-fs.

Mixing up 'writeFile' and 'readFile' methods.

To create a directory use 'mkdir', to write a file use 'writeFile', and to read a file use 'readFile' in react-native-fs.

Practice

1. What is the main purpose of using react-native-fs in a React Native app?

easy

A. To read and write files on the device's file system

B. To create user interface components

C. To manage app navigation between screens

D. To handle network requests and API calls

Solution

1. Step 1: Understand the role of react-native-fs

   This library is designed to provide file system access in React Native apps.

2. Step 2: Identify the correct functionality

   It allows reading and writing files on the device, unlike UI or network libraries.

3. Final Answer:

   To read and write files on the device's file system -> Option A

4. Quick Check:

   File system access = read/write files [OK]

Hint: Remember: react-native-fs is for file operations only [OK]

Common Mistakes:

• Confusing file system access with UI components
• Thinking it manages navigation or network calls
• Assuming it handles permissions automatically

2. Which of the following is the recommended ES6 import syntax for react-native-fs in a React Native file?

easy

A. import * as RNFS from 'react-native-fs';

B. import RNFS from 'react-native-fs';

C. import { RNFS } from 'react-native-fs';

D. const RNFS = require('react-native-fs');

Solution

1. Step 1: Recall ES6 import syntax for default exports

   react-native-fs exports a default object, so use import RNFS from 'react-native-fs';.

2. Step 2: Check other options

   const RNFS = require('react-native-fs'); uses CommonJS require (valid but less common in modern React Native). import { RNFS } from 'react-native-fs'; incorrectly destructures. import * as RNFS from 'react-native-fs'; imports all as namespace but is not the recommended style here.

3. Final Answer:

   import RNFS from 'react-native-fs'; -> Option B

4. Quick Check:

   Default import syntax = import RNFS from 'react-native-fs'; [OK]

Hint: Use default import for react-native-fs: import RNFS from '...' [OK]

Common Mistakes:

• Using destructuring import for default export
• Mixing require and import styles
• Using namespace import unnecessarily

3. What will the following code output if the file test.txt contains the text "Hello World"?

import RNFS from 'react-native-fs';

RNFS.readFile(RNFS.DocumentDirectoryPath + '/test.txt', 'utf8')
  .then(contents => console.log(contents))
  .catch(err => console.log('Error:', err.message));

medium

A. Error: File not found

B. An empty string

C. undefined

D. "Hello World"

Solution

1. Step 1: Understand readFile behavior

   The readFile method reads the file content as a string when encoding is 'utf8'.

2. Step 2: Check file content and output

   The file contains "Hello World", so the promise resolves and logs this string.

3. Final Answer:

   "Hello World" -> Option D

4. Quick Check:

   readFile with utf8 returns file text [OK]

Hint: readFile with 'utf8' returns file text content [OK]

Common Mistakes:

• Assuming readFile returns a buffer or object
• Expecting error if file exists
• Ignoring promise and expecting synchronous output

4. Identify the error in this code snippet that tries to write text to a file:

import RNFS from 'react-native-fs';

RNFS.writeFile('/path/to/file.txt', 'Sample text', 'utf8')
  .then(() => console.log('File written'))
  .catch(error => console.log('Write error:', error));

medium

A. The file path should use RNFS.DocumentDirectoryPath or similar, not an absolute string

B. The encoding 'utf8' is not supported by writeFile

C. writeFile does not return a promise

D. The text argument must be an object, not a string

Solution

1. Step 1: Check file path usage

   In React Native, absolute paths like '/path/to/file.txt' are invalid; use RNFS.DocumentDirectoryPath or similar directory constants.

2. Step 2: Validate other parameters

   Encoding 'utf8' is valid, writeFile returns a promise, and text can be a string.

3. Final Answer:

   The file path should use RNFS.DocumentDirectoryPath or similar, not an absolute string -> Option A

4. Quick Check:

   Use RNFS paths, not absolute strings [OK]

Hint: Always use RNFS directory constants for file paths [OK]

Common Mistakes:

• Using absolute file paths directly
• Misunderstanding writeFile return type
• Passing wrong data types for text

5. You want to save user notes in a file and then read them back later. Which approach correctly handles permissions, writes the file, and reads it back safely in React Native using react-native-fs?

hard

A. Use fetch API to write and read files on device storage

B. Write file directly to '/storage/emulated/0/notes.txt' without permission, then read it

C. Request storage permission, write file using RNFS.DocumentDirectoryPath, then read file with error handling

D. Write file with no encoding specified, then read file with 'ascii' encoding

Solution

1. Step 1: Handle permissions properly

   On mobile devices, storage permission must be requested before file operations.

2. Step 2: Use safe file paths and encoding

   Use RNFS.DocumentDirectoryPath for file location and specify encoding like 'utf8' for writing and reading.

3. Step 3: Implement error handling

   Use promises with then and catch to handle success and errors safely.

4. Final Answer:

   Request storage permission, write file using RNFS.DocumentDirectoryPath, then read file with error handling -> Option C

5. Quick Check:

   Permissions + RNFS paths + error handling = Request storage permission, write file using RNFS.DocumentDirectoryPath, then read file with error handling [OK]

Hint: Always request permission and use RNFS paths with error handling [OK]

Common Mistakes:

• Skipping permission requests
• Using hardcoded absolute paths
• Ignoring promise errors
• Using wrong encoding for text files