Checking file existence and stats in Node.js - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Node.js code snippet?

Consider the following code that checks if a file exists and prints its size in bytes:

Node.js

import { promises as fs } from 'fs';

async function checkFile() {
  try {
    await fs.access('example.txt');
    const stats = await fs.stat('example.txt');
    console.log(`Size: ${stats.size}`);
  } catch {
    console.log('File does not exist');
  }
}

checkFile();

A Prints 'Size: 0' if 'example.txt' is empty, or 'File does not exist' if missing

B Always prints 'File does not exist' regardless of file presence

C Throws a runtime error if 'example.txt' does not exist

D Prints 'Size: undefined' if the file exists

💡 Hint

Check what fs.access and fs.stat do and how errors are handled in async/await.

The code uses fs.access to check if the file exists. If it does, fs.stat returns stats including size. If the file is missing, the catch block prints 'File does not exist'.

❓ component_behavior

intermediate

What happens when using fs.existsSync to check a file synchronously?

Given this code snippet:

Node.js

import fs from 'fs';

if (fs.existsSync('data.json')) {
  console.log('File found');
} else {
  console.log('File missing');
}

A Always prints 'File missing' because existsSync is deprecated

B Prints 'File found' if 'data.json' exists, otherwise 'File missing'

C Throws an error if 'data.json' does not exist

D Prints 'File found' even if the file is missing

💡 Hint

Check the behavior of fs.existsSync in Node.js.

fs.existsSync returns true if the file exists, false otherwise. It does not throw errors.

📝 Syntax

advanced

Which option correctly uses fs.promises.stat to get file stats?

Choose the code snippet that correctly gets file stats asynchronously and logs the file size:

A await fs.stat('file.txt', (err, stats) => { console.log(stats.size); });

B fs.promises.stat('file.txt', (err, stats) => { console.log(stats.size); });

C const stats = fs.promises.stat('file.txt'); console.log(stats.size);

D const stats = await fs.promises.stat('file.txt'); console.log(stats.size);

💡 Hint

Remember that fs.promises methods return promises and do not use callbacks.

Option D correctly awaits the promise returned by fs.promises.stat and accesses size. Option D and D incorrectly mix callbacks with promises. Option D does not await the promise, so stats.size is undefined.

🔧 Debug

advanced

Why does this code throw an error when checking file stats?

Analyze this code snippet:

Node.js

import fs from 'fs';

fs.stat('missing.txt', (err, stats) => {
  if (stats.size > 0) {
    console.log('File has content');
  }
});

A It throws because the callback is missing the error check for 'err'

B It throws because fs.stat requires promises, not callbacks

C It throws because stats is undefined when the file is missing, causing 'stats.size' to fail

D It throws because 'missing.txt' is a directory, not a file

💡 Hint

What happens if the file does not exist? What is the value of stats?

If the file is missing, err is set and stats is undefined. Accessing stats.size causes a TypeError.

🧠 Conceptual

expert

What is the difference between fs.access and fs.stat when checking file existence?

Select the most accurate statement about fs.access and fs.stat:

A fs.access checks permissions and existence without returning file info; fs.stat returns detailed file info but throws if file missing

B fs.access returns file size; fs.stat only checks if file exists

C fs.access throws an error if file exists; fs.stat never throws errors

D fs.access is synchronous only; fs.stat is asynchronous only

💡 Hint

Think about what each function is designed to do and their error behavior.

fs.access tests if the file can be accessed with given permissions and does not return stats. fs.stat returns detailed info but throws if file is missing.

Practice

1. Which Node.js method is best to check if a file exists without throwing an error?

easy

A. fs.writeFile

B. fs.readFile

C. fs.open

D. fs.access

Solution

1. Step 1: Understand file existence check methods

   fs.access is designed to check file accessibility without opening or reading it.

2. Step 2: Compare with other methods

   fs.readFile reads content, fs.open opens file descriptor, fs.writeFile writes data. These are not meant for existence check.

3. Final Answer:

   fs.access -> Option D

4. Quick Check:

   Check file existence = fs.access [OK]

Hint: Use fs.access to check file existence safely [OK]

Common Mistakes:

• Using fs.readFile which throws error if file missing
• Trying fs.writeFile which creates or overwrites file
• Using fs.open without error handling

2. Which of the following is the correct syntax to get file stats synchronously in Node.js?

easy

A. fs.statSync('file.txt')

B. fs.stat('file.txt')

C. fs.getStatsSync('file.txt')

D. fs.fileStats('file.txt')

Solution

1. Step 1: Identify synchronous stat method

   fs.statSync is the synchronous method to get file stats.

2. Step 2: Check other options

   fs.stat is asynchronous, others are invalid method names.

3. Final Answer:

   fs.statSync('file.txt') -> Option A

4. Quick Check:

   Synchronous file stats = fs.statSync [OK]

Hint: Sync methods end with Sync, like fs.statSync [OK]

Common Mistakes:

• Confusing async fs.stat with sync fs.statSync
• Using non-existent methods like fs.getStatsSync
• Missing parentheses for function call

3. What will the following code output if 'example.txt' exists and is a file of size 1024 bytes?

const fs = require('fs');
fs.stat('example.txt', (err, stats) => {
  if (err) return console.error('Error');
  console.log(stats.isFile(), stats.size);
});

medium

A. true 1024

B. false 1024

C. true undefined

D. Error

Solution

1. Step 1: Understand fs.stat callback

   If file exists, err is null and stats object contains file info.

2. Step 2: Check stats properties

   stats.isFile() returns true if it is a file, stats.size returns file size in bytes.

3. Final Answer:

   true 1024 -> Option A

4. Quick Check:

   File exists and is file = true and size = 1024 [OK]

Hint: stats.isFile() true means file exists, size shows bytes [OK]

Common Mistakes:

• Assuming stats.size is undefined
• Confusing isFile() with isDirectory()
• Not handling error callback properly

4. Identify the error in this code snippet that checks if a file exists:

const fs = require('fs');
try {
  fs.access('data.txt');
  console.log('File exists');
} catch (err) {
  console.log('File does not exist');
}

medium

A. fs.access does not check file existence

B. fs.access is asynchronous and needs a callback or promise

C. Try/catch cannot catch errors in Node.js

D. console.log syntax is incorrect

Solution

1. Step 1: Check fs.access usage

   fs.access is asynchronous and requires a callback or promise to handle errors.

2. Step 2: Understand try/catch with async

   Try/catch does not catch errors from async calls without await or callback handling.

3. Final Answer:

   fs.access is asynchronous and needs a callback or promise -> Option B

4. Quick Check:

   Async fs.access needs callback/promise [OK]

Hint: Async functions need callbacks or await, not try/catch alone [OK]

Common Mistakes:

• Assuming try/catch works with async without await
• Ignoring callback parameter in fs.access
• Thinking fs.access does not check existence

5. You want to write a function that returns true if a given path is a directory and exists, false otherwise. Which code snippet correctly implements this using Node.js synchronous methods?

hard

A. function isDirectory(path) {
if (fs.statSync(path).isDirectory()) return true;
else return false;
}

B. function isDirectory(path) {
return fs.accessSync(path) && fs.statSync(path).isDirectory();
}

C. function isDirectory(path) {
try {
return fs.statSync(path).isDirectory();
} catch {
return false;
}
}

D. function isDirectory(path) {
try {
return fs.existsSync(path) && fs.statSync(path).isFile();
} catch {
return false;
}
}

Solution

1. Step 1: Check for existence and directory type safely

   Using fs.statSync inside try/catch handles missing path errors and checks if it's a directory.

2. Step 2: Analyze other options

   function isDirectory(path) { return fs.accessSync(path) && fs.statSync(path).isDirectory(); } misuses fs.accessSync without error handling; function isDirectory(path) { try { return fs.existsSync(path) && fs.statSync(path).isFile(); } catch { return false; } } checks isFile() instead of isDirectory(); function isDirectory(path) { if (fs.statSync(path).isDirectory()) return true; else return false; } lacks error handling for missing path.

3. Final Answer:

   function isDirectory(path) { try { return fs.statSync(path).isDirectory(); } catch { return false; } } -> Option C

4. Quick Check:

   Try/catch with statSync and isDirectory() = correct [OK]

Hint: Use try/catch with fs.statSync and isDirectory() to check safely [OK]

Common Mistakes:

• Not handling errors for missing paths
• Checking isFile() instead of isDirectory()
• Using fs.accessSync without try/catch