Why file system access matters in Node.js - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the Node.js file system module.

Node.js

const fs = require([1]);

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

A"fs"

B"path"

C"http"

D"os"

Attempts:

3 left

💡 Hint

Common Mistakes

Using other module names like "path" or "http" which do not provide file system access.

The fs module is the built-in Node.js module to access the file system. You import it with require("fs").

2fill in blank

medium

Complete the code to read a file asynchronously using the fs module.

Node.js

fs.readFile('example.txt', 'utf8', (err, data) => {
  if (err) throw err;
  console.log([1]);
});

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

Adata

Berr

Cfs

Dconsole

Attempts:

3 left

💡 Hint

Common Mistakes

Logging err instead of data.

Trying to log fs or console which are not file content.

The data parameter contains the file content read by fs.readFile. You log data to see the file content.

3fill in blank

hard

Fix the error in the code to write data to a file asynchronously.

Node.js

fs.writeFile('output.txt', [1], (err) => {
  if (err) throw err;
  console.log('File saved!');
});

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

Aconsole.log

Bfs

Cundefined

Ddata

Attempts:

3 left

💡 Hint

Common Mistakes

Passing fs or console.log instead of the data string.

Passing undefined which causes an error.

The second argument to fs.writeFile must be the data to write. Using data correctly writes the content.

4fill in blank

hard

Fill both blanks to create a directory and then read its contents.

Node.js

fs.[1]('myFolder', (err) => {
  if (err) throw err;
  fs.[2]('myFolder', (err, files) => {
    if (err) throw err;
    console.log(files);
  });
});

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

Amkdir

BreadFile

Creaddir

Dunlink

Attempts:

3 left

💡 Hint

Common Mistakes

Using readFile which reads file content, not directory contents.

Using unlink which deletes files.

mkdir creates a directory. readdir reads the contents of a directory. Together they create and list files in 'myFolder'.

5fill in blank

hard

Fill all three blanks to check if a file exists, then read it if it does.

Node.js

fs.[1]('data.txt', (err) => {
  if (!err) {
    fs.[2]('data.txt', 'utf8', (err, [3]) => {
      if (err) throw err;
      console.log([3]);
    });
  } else {
    console.log('File does not exist');
  }
});

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

Aaccess

BreadFile

Cdata

DwriteFile

Attempts:

3 left

💡 Hint

Common Mistakes

Using writeFile instead of readFile to read content.

Not checking if the file exists before reading.

fs.access checks if the file exists. If no error, fs.readFile reads the file. The content is stored in data and logged.

Practice

1. Why is file system access important in a Node.js application?

easy

A. It prevents the app from using the internet.

B. It makes the app run faster by using more CPU cores.

C. It automatically fixes bugs in the code.

D. It allows the app to save and load data outside the program.

Solution

1. Step 1: Understand file system role

   File system access lets an app save and retrieve data from files on the computer.

2. Step 2: Identify correct purpose

   Only 'It allows the app to save and load data outside the program.' correctly describes this purpose; others are unrelated to file system access.

3. Final Answer:

   It allows the app to save and load data outside the program. -> Option D

4. Quick Check:

   File system access = save/load data [OK]

Hint: File system means saving or reading files outside code [OK]

Common Mistakes:

• Confusing file system access with CPU or internet features
• Thinking file system fixes bugs automatically
• Assuming file system access speeds up CPU usage

2. Which of the following is the correct way to import the Node.js file system module?

easy

A. require fs from 'fs';

B. const fs = require('fs');

C. const fs = import('fs');

D. import fs from 'fs';

Solution

1. Step 1: Recall Node.js import syntax

   Node.js commonly uses const fs = require('fs'); to import modules in CommonJS style.

2. Step 2: Check options for syntax correctness

   'require fs from 'fs';' is invalid syntax; 'import fs from 'fs';' is ES module style but requires extra config; 'const fs = import('fs');' uses dynamic import returning a Promise; 'const fs = require('fs');' matches correct syntax.

3. Final Answer:

   const fs = require('fs'); -> Option B

4. Quick Check:

   CommonJS import = require('fs') [OK]

Hint: Use require('fs') to import file system in Node.js [OK]

Common Mistakes:

• Using ES module import without config
• Writing invalid syntax like 'require fs from'
• Confusing import() function with require()

3. What will the following Node.js code output?

const fs = require('fs');
fs.writeFileSync('test.txt', 'Hello');
const data = fs.readFileSync('test.txt', 'utf8');
console.log(data);

medium

A. Error: File not found

B. undefined

C. Hello

D. null

Solution

1. Step 1: Write data to file synchronously

   The code writes 'Hello' to 'test.txt' using writeFileSync, which blocks until done.

2. Step 2: Read file content synchronously

   Then it reads the file content as UTF-8 text and stores it in data.

3. Step 3: Output the read content

   console.log prints the string 'Hello' read from the file.

4. Final Answer:

   Hello -> Option C

5. Quick Check:

   Write then read file = 'Hello' output [OK]

Hint: WriteFileSync then ReadFileSync outputs written text [OK]

Common Mistakes:

• Assuming async functions without callbacks
• Expecting undefined or null instead of file content
• Thinking file read fails without prior write

4. Identify the error in this Node.js code snippet:

const fs = require('fs');
fs.readFile('data.txt', (err, data) => {
  if (err) throw err;
  console.log(data);
});

medium

A. Missing encoding, so data is a Buffer, not string.

B. Callback function is missing the error parameter.

C. readFile is a synchronous method, cannot use callback.

D. fs module is not imported correctly.

Solution

1. Step 1: Check readFile usage

   fs.readFile without encoding returns a Buffer object, not a string.

2. Step 2: Understand console.log output

   Logging Buffer prints raw bytes, not readable text. To get string, encoding like 'utf8' is needed.

3. Final Answer:

   Missing encoding, so data is a Buffer, not string. -> Option A

4. Quick Check:

   readFile without encoding = Buffer data [OK]

Hint: Add 'utf8' encoding to readFile for string data [OK]

Common Mistakes:

• Ignoring that data is a Buffer without encoding
• Thinking readFile is synchronous
• Assuming callback lacks error parameter

5. You want to read multiple files asynchronously and process their contents only after all are read. Which approach best uses Node.js file system access to achieve this?

hard

A. Use fs.readFile with callbacks and count completed reads before processing.

B. Use fs.readFileSync for each file in a loop to block until done.

C. Use fs.writeFile to write all files first, then read one file.

D. Use fs.unlink to delete files before reading them.

Solution

1. Step 1: Understand asynchronous reading need

   Reading files asynchronously avoids blocking the app and keeps it responsive.

2. Step 2: Choose method to track multiple async reads

   Using fs.readFile with callbacks and counting completions lets you know when all files are read before processing.

3. Step 3: Eliminate incorrect options

   Using fs.readFileSync for each file in a loop blocks until done and is inefficient; using fs.writeFile writes files unnecessarily; using fs.unlink deletes files, which is wrong.

4. Final Answer:

   Use fs.readFile with callbacks and count completed reads before processing. -> Option A

5. Quick Check:

   Async read with callbacks + count = best approach [OK]

Hint: Use async readFile with callback counting to wait all done [OK]

Common Mistakes:

• Using synchronous reads blocking the app
• Confusing writeFile with reading files
• Deleting files before reading them