Reading files synchronously in Node.js - Mini Project: Build & Apply

Reading files synchronously

📖 Scenario: You are building a simple Node.js script that reads the contents of a text file to display its data.

🎯 Goal: Learn how to read a file synchronously using Node.js built-in fs module and store its content in a variable.

📋 What You'll Learn

Use the Node.js fs module

Read the file example.txt synchronously

Store the file content in a variable called fileContent

Use UTF-8 encoding to read the file as text

💡 Why This Matters

🌍 Real World

Reading configuration files or data files synchronously is common in scripts that need to load settings before running.

💼 Career

Understanding how to read files synchronously is important for backend developers working with Node.js to manage file data reliably.

1

Import the fs module

Write a line to import the Node.js fs module using require and assign it to a variable called fs.

Node.js

# Import the fs module
# Your code here

Hint

Use const fs = require('fs'); to import the file system module.

2

Create a variable for the file path

Create a variable called filePath and set it to the string 'example.txt' which is the file you want to read.

Node.js

const fs = require('fs');
# Create a variable filePath with value 'example.txt'
# Your code here

Hint

Use const filePath = 'example.txt'; to store the file name.

3

Read the file content synchronously

Use fs.readFileSync with filePath and encoding 'utf8' to read the file content synchronously. Store the result in a variable called fileContent.

Node.js

const fs = require('fs');
const filePath = 'example.txt';
# Read the file synchronously and store in fileContent
# Your code here

Hint

Use const fileContent = fs.readFileSync(filePath, 'utf8'); to read the file as text.

4

Export the file content variable

Add a line to export the fileContent variable using module.exports so other files can use it.

Node.js

const fs = require('fs');
const filePath = 'example.txt';
const fileContent = fs.readFileSync(filePath, 'utf8');
# Export fileContent using module.exports
# Your code here

Hint

Use module.exports = fileContent; to export the variable.

Practice

1. What does reading a file synchronously in Node.js mean?

easy

A. The file is read only if the program is connected to the internet.

B. The program waits until the file is fully read before moving on.

C. The file is read in the background while the program continues.

D. The file is read multiple times at once to speed up reading.

Solution

1. Step 1: Understand synchronous reading

   Reading a file synchronously means the program pauses and waits for the file to be fully read before continuing.

2. Step 2: Compare with asynchronous reading

   Asynchronous reading allows the program to continue running while the file is being read, which is not the case here.

3. Final Answer:

   The program waits until the file is fully read before moving on. -> Option B

4. Quick Check:

   Synchronous reading = wait for file read [OK]

Hint: Synchronous means wait until done before next step [OK]

Common Mistakes:

• Confusing synchronous with asynchronous reading
• Thinking file reads happen in parallel automatically
• Assuming synchronous reading is faster

2. Which of the following is the correct way to read a file synchronously using Node.js's fs module?

easy

A. const data = fs.readSync('file.txt');

B. const data = fs.readFile('file.txt');

C. const data = fs.readFileAsync('file.txt');

D. const data = fs.readFileSync('file.txt', 'utf8');

Solution

1. Step 1: Identify the synchronous read method

   Node.js's fs module provides readFileSync() to read files synchronously.

2. Step 2: Check method usage and parameters

   readFileSync requires the file path and optionally encoding like 'utf8' to get a string.

3. Final Answer:

   const data = fs.readFileSync('file.txt', 'utf8'); -> Option D

4. Quick Check:

   readFileSync is synchronous read method [OK]

Hint: Use readFileSync with encoding for synchronous read [OK]

Common Mistakes:

• Using readFile instead of readFileSync for sync reading
• Missing encoding parameter to get string output
• Using non-existent methods like readFileAsync or readSync

3. What will be the output of this code snippet?

const fs = require('fs');
const content = fs.readFileSync('example.txt', 'utf8');
console.log(typeof content);

medium

A. 'string'

B. 'buffer'

C. 'undefined'

D. 'object'

Solution

1. Step 1: Understand readFileSync output with encoding

   When readFileSync is called with 'utf8' encoding, it returns a string containing the file content.

2. Step 2: Check typeof operator on string

   typeof on a string returns 'string'.

3. Final Answer:

   'string' -> Option A

4. Quick Check:

   readFileSync with 'utf8' returns string [OK]

Hint: readFileSync with 'utf8' returns string type [OK]

Common Mistakes:

• Assuming output is a Buffer without encoding
• Confusing typeof output with file content
• Expecting 'object' or 'buffer' instead of 'string'

4. Identify the error in this code snippet that reads a file synchronously:

const data = fs.readFileSync('data.txt');
console.log(data.toString('utf8'));

medium

A. fs module is not imported correctly.

B. toString() should not have 'utf8' as argument here.

C. Missing encoding in readFileSync causes error.

D. readFileSync requires a callback function.

Solution

1. Step 1: Check the import statement

   The code snippet is missing the line to import the fs module: const fs = require('fs');

2. Step 2: Consequence of missing import

   Without importing fs, fs.readFileSync will throw ReferenceError: fs is not defined.

3. Step 3: Why other options are incorrect

   A: readFileSync is synchronous, no callback needed.
   B: Without encoding, returns Buffer; Buffer.toString('utf8') is valid.
   C: Missing encoding returns Buffer, no error.

4. Final Answer:

   fs module is not imported correctly. -> Option A

5. Quick Check:

   Missing fs import causes ReferenceError [OK]

Hint: Require 'fs' module before using fs methods [OK]

Common Mistakes:

• Thinking readFileSync needs a callback
• Assuming missing encoding causes error
• Believing toString cannot take encoding argument

5. You want to read a small configuration file synchronously and handle errors properly. Which code snippet correctly does this?

hard

A. const fs = require('fs');
const config = fs.readFileSync('config.json');
console.log(config.toString());

B. const fs = require('fs');
const config = fs.readFileSync('config.json', 'utf8', (err, data) => {
if (err) throw err;
console.log(data);
});

C. const fs = require('fs');
try {
const config = fs.readFileSync('config.json', 'utf8');
console.log(config);
} catch (err) {
console.error('Error reading file:', err.message);
}

D. const fs = require('fs');
fs.readFileSync('config.json', 'utf8').then(data => console.log(data));

Solution

1. Step 1: Use try-catch to handle errors in synchronous reading

   Since readFileSync throws errors on failure, wrapping it in try-catch is necessary to handle errors gracefully.

2. Step 2: Check each option for correctness

   const fs = require('fs'); try { const config = fs.readFileSync('config.json', 'utf8'); console.log(config); } catch (err) { console.error('Error reading file:', err.message); } uses try-catch correctly and reads file synchronously with encoding. const fs = require('fs'); const config = fs.readFileSync('config.json', 'utf8', (err, data) => { if (err) throw err; console.log(data); }); incorrectly uses a callback with readFileSync which does not accept callbacks. const fs = require('fs'); const config = fs.readFileSync('config.json'); console.log(config.toString()); reads without encoding and does not handle errors. const fs = require('fs'); fs.readFileSync('config.json', 'utf8').then(data => console.log(data)); incorrectly uses then() on readFileSync which returns data directly, not a promise.

3. Final Answer:

   const fs = require('fs'); try { const config = fs.readFileSync('config.json', 'utf8'); console.log(config); } catch (err) { console.error('Error reading file:', err.message); } -> Option C

4. Quick Check:

   Use try-catch with readFileSync for error handling [OK]

Hint: Wrap readFileSync in try-catch to catch errors [OK]

Common Mistakes:

• Using callbacks with readFileSync
• Not handling errors causing crashes
• Using promises with synchronous methods