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.