Reading and Writing Files in Node.js

Introduction to Reading and Writing Files Using fs Module in Node.js

In Node.js, the fs (file system) module allows you to interact with the file system on your machine. This includes reading and writing files, which can be essential for various applications, such as configuration management, data storage, and logging. In this guide, we’ll walk through three diverse examples that demonstrate how to read from and write to files using the fs module.

Example 1: Reading a Text File

Context

This example shows how to read a simple text file, which might contain configuration settings or user data. Reading files is a common task when you want to retrieve information stored in a file format.

Code Example

const fs = require('fs');

// Read a file asynchronously
fs.readFile('example.txt', 'utf8', (err, data) => {
    if (err) {
        console.error('Error reading the file:', err);
        return;
    }
    console.log('File contents:', data);
});

Notes

• Ensure that the example.txt file exists in the same directory as your script, or provide the correct path.
• The utf8 encoding is specified to ensure the text is read correctly as a string.
• This example uses an asynchronous approach, which is non-blocking and allows other operations to continue while the file is being read.

Example 2: Writing to a JSON File

Context

In many applications, you’ll need to save data in JSON format. This example demonstrates how to write an object to a file as JSON. This is particularly useful for saving settings or user preferences.

Code Example

const fs = require('fs');
const data = {
    name: 'John Doe',
    age: 30,
    city: 'New York'
};

// Convert object to JSON and write to a file
fs.writeFile('data.json', JSON.stringify(data, null, 2), (err) => {
    if (err) {
        console.error('Error writing to file:', err);
        return;
    }
    console.log('Data successfully written to data.json');
});

Notes

• The JSON.stringify(data, null, 2) method converts the JavaScript object to a JSON string, with indentation for readability.
• If the data.json file does not exist, it will be created automatically.
• This is also an asynchronous operation, ensuring that your application remains responsive.

Example 3: Appending Data to a File

Context

Sometimes, you may need to add new data to an existing file without overwriting it. This example demonstrates how to append text to a log file, which can be useful for maintaining application logs.

Code Example

const fs = require('fs');
const logEntry = 'User logged in at: ' + new Date().toISOString() + '\n';

// Append to a file
fs.appendFile('log.txt', logEntry, (err) => {
    if (err) {
        console.error('Error appending to file:', err);
        return;
    }
    console.log('Log entry added successfully');
});

Notes

• The log.txt file will be created if it doesn’t already exist, and new log entries will be added at the end of the file.
• This example uses new Date().toISOString() to generate a timestamp for the log entry, ensuring each entry is time-stamped.
• As with previous examples, this method is asynchronous, allowing for efficient file handling without blocking other processes.