Reading files asynchronously with callbacks in Node.js - Mini Project: Build & Apply

Reading files asynchronously with callbacks in Node.js

📖 Scenario: You are building a simple Node.js script that reads the content of a text file asynchronously. This is useful when you want your program to keep working without waiting for the file to finish loading.

🎯 Goal: Learn how to read a file asynchronously using Node.js fs module with callbacks. You will create a script that reads a file named message.txt and prints its content inside the callback function.

📋 What You'll Learn

Use Node.js built-in fs module

Read the file message.txt asynchronously using fs.readFile

Use a callback function to handle the file content or error

Print the file content inside the callback

💡 Why This Matters

🌍 Real World

Reading files asynchronously is common in Node.js servers to avoid blocking the program while waiting for file data, improving performance and user experience.

💼 Career

Understanding asynchronous file reading with callbacks is essential for backend developers working with Node.js, enabling efficient file handling in real applications.

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

Need a hint?

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

2

Create a variable for the filename

Create a constant variable called filename and set it to the string 'message.txt'.

Node.js

const fs = require('fs');
# Create a variable called filename with value 'message.txt'
# Your code here

Need a hint?

Use const filename = 'message.txt'; to store the file name.

3

Read the file asynchronously with a callback

Use fs.readFile with filename, encoding 'utf8', and a callback function with parameters err and data. Inside the callback, if err is not null, return immediately. Otherwise, log data to the console.

Node.js

const fs = require('fs');
const filename = 'message.txt';

# Use fs.readFile with filename, 'utf8', and a callback function (err, data)
# Inside callback, if err exists return, else console.log data
# Your code here

Need a hint?

Use fs.readFile(filename, 'utf8', (err, data) => { ... }) and handle error by returning early.

4

Add error message logging inside the callback

Modify the callback function so that if err exists, it logs 'Error reading file' to the console before returning.

Node.js

const fs = require('fs');
const filename = 'message.txt';

fs.readFile(filename, 'utf8', (err, data) => {
    # If err exists, log 'Error reading file' and return
    # Your code here
    console.log(data);
});

Need a hint?

Inside the callback, check if (err) { console.log('Error reading file'); return; }.