Appending to files in Node.js - Mini Project: Build & Apply

Appending Text to a File in Node.js

📖 Scenario: You are building a simple Node.js script to keep a log of user actions. Each time a user performs an action, you want to add a new line to a log file without deleting the old entries.

🎯 Goal: Create a Node.js script that appends a new log entry to an existing file called userlog.txt. If the file does not exist, it should be created automatically.

📋 What You'll Learn

Use the built-in fs module to work with files

Create a variable called logEntry with the exact string 'User logged in\n'

Create a variable called filename with the exact string 'userlog.txt'

Use fs.appendFile to add logEntry to filename

Handle errors by logging 'Error writing to file' if any occur

💡 Why This Matters

🌍 Real World

Appending to log files is common in real applications to keep track of user actions, errors, or system events without losing previous data.

💼 Career

Understanding how to work with files and handle asynchronous operations in Node.js is essential for backend development and building reliable server-side applications.

1

Set up the log entry text

Create a variable called logEntry and set it to the string 'User logged in\n' exactly.

Node.js

# Create a variable called logEntry with the string 'User logged in\n'
# Your code here

Need a hint?

Use const to declare logEntry and include the newline character \n at the end.

2

Set the filename variable

Create a variable called filename and set it to the string 'userlog.txt' exactly.

Node.js

const logEntry = 'User logged in\n';
# Create a variable called filename with the string 'userlog.txt'
# Your code here

Need a hint?

Use const to declare filename with the exact string.

3

Import the fs module

Add a line at the top to import the built-in fs module using import fs from 'fs';.

Node.js

# Import the fs module
import fs from 'fs';

const logEntry = 'User logged in\n';
const filename = 'userlog.txt';
# Your code here

Need a hint?

Use ES module syntax to import fs.

4

Append the log entry to the file

Use fs.appendFile to add logEntry to filename. Provide a callback that logs 'Error writing to file' if an error occurs.

Node.js

import fs from 'fs';

const logEntry = 'User logged in\n';
const filename = 'userlog.txt';

// Append logEntry to filename
# Your code here

Need a hint?

Use fs.appendFile(filename, logEntry, callback) and check if err is truthy inside the callback.