Reading files synchronously in Node.js - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this synchronous file read code?

Consider the following Node.js code snippet that reads a file synchronously. What will be printed to the console?

Node.js

import fs from 'fs';
const data = fs.readFileSync('example.txt', 'utf8');
console.log(typeof data);

A "undefined"

B "string"

C "Buffer"

D "object"

💡 Hint

The encoding option affects the type of the returned data.

When you specify 'utf8' encoding in readFileSync, the returned data is a string.

Without encoding, it returns a Buffer object.

❓ component_behavior

intermediate

What happens if the file does not exist in synchronous read?

Given this code snippet, what will happen if 'missing.txt' does not exist?

Node.js

import fs from 'fs';
try {
  const content = fs.readFileSync('missing.txt', 'utf8');
  console.log(content);
} catch (err) {
  console.log('Error caught');
}

A It prints an empty string.

B It prints 'undefined'.

C The catch block runs and prints 'Error caught'.

D The program crashes with an uncaught error.

💡 Hint

Synchronous read throws an error if the file is missing.

readFileSync throws an error if the file is not found.

The try...catch block catches this error and prints 'Error caught'.

📝 Syntax

advanced

Which option correctly reads a file synchronously with UTF-8 encoding?

Select the code snippet that correctly reads 'data.txt' synchronously as a UTF-8 string.

A const content = fs.readFileSync('data.txt', 'utf8');

B const content = fs.readFileSync('data.txt', 'utf-8');

C const content = fs.readFileSync('data.txt', {encoding: 'utf8'});

D const content = fs.readFileSync('data.txt', {encoding: 'utf-8'});

💡 Hint

Check the exact spelling and case of encoding options.

Options A and C use the correct encoding 'utf8' which is accepted by Node.js.

Options B and D use 'utf-8' with a dash, which is not recognized and causes an error.

🔧 Debug

advanced

Why does this synchronous read code throw an error?

Identify the cause of the error in this code snippet:

Node.js

import fs from 'fs';
const content = fs.readFileSync('file.txt');
console.log(content.toString('utf8'));

A readFileSync returns a string, so calling toString with encoding causes an error.

B toString does not accept encoding as argument, causing a TypeError.

C Missing encoding in readFileSync causes a syntax error.

D readFileSync returns a Buffer by default, so toString with encoding is valid and no error occurs.

💡 Hint

Check what type readFileSync returns when encoding is not specified.

Without specifying encoding, readFileSync returns a Buffer.

Buffer's toString method accepts an encoding argument, so this code works without error.

🧠 Conceptual

expert

How does synchronous file reading affect Node.js event loop?

Choose the correct statement about synchronous file reading in Node.js.

A Synchronous file reading blocks the event loop, pausing all other operations until complete.

B Synchronous file reading runs in a separate thread, so it does not block the event loop.

C Synchronous file reading queues the read operation and continues immediately without blocking.

D Synchronous file reading only blocks the current callback but allows other events to process.

💡 Hint

Think about what 'synchronous' means for single-threaded Node.js.

Synchronous operations block the main thread in Node.js, stopping all other JavaScript execution until they finish.

This means the event loop is paused during synchronous file reads.