Reading and Writing Files in Node.js

1. Introduction

This tutorial aims to provide a step-by-step guide to reading and writing files in Node.js. We'll use the built-in fs (file system) module in Node.js to open, read, write, and close files.

By the end of this tutorial, you'll learn:

• How to include the fs module in your Node.js application
• How to read files using the fs module
• How to write to files using the fs module

Prerequisites: Basic understanding of JavaScript and Node.js.

2. Step-by-Step Guide

The fs module in Node.js is designed to work with the file system on your computer. It allows you to work with files on your server, including creating, reading, updating, deleting, and renaming files.

Including the fs Module

To use the fs module, you need to require it in your application:

const fs = require('fs');

Reading Files

To read the content of a file, use the fs.readFile() function. This function reads the entire file and then calls the callback function with the file content:

fs.readFile('example.txt', 'utf8', function(err, data) {
  if (err) throw err;
  console.log(data);
});

Writing Files

To write to a file, use the fs.writeFile() function. If the file does not exist, it will be created:

fs.writeFile('example.txt', 'Hello, World!', function(err) {
  if (err) throw err;
  console.log('File written!');
});

3. Code Examples

Reading a File

const fs = require('fs');

// Read the file
fs.readFile('example.txt', 'utf8', (err, data) => {
  if (err) {
    console.error('An error occurred:', err);
    return;
  }
  // The file data is a string
  console.log('File content:', data);
});

In this code snippet, we read the file example.txt and then log its contents to the console. If an error occurs (for example, if the file does not exist), we log the error message.

Writing a File

const fs = require('fs');

// Write to the file
fs.writeFile('example.txt', 'Hello, World!', (err) => {
  if (err) {
    console.error('An error occurred:', err);
    return;
  }
  console.log('File written successfully!');
});

In this code snippet, we write the string Hello, World! to the file example.txt. If the file does not exist, it will be created. If an error occurs, we log the error message.

4. Summary

In this tutorial, we learned how to read and write files in Node.js using the fs module. We've covered how to include the fs module in your application and use its readFile() and writeFile() functions to interact with files.

For further learning, explore other fs functions, such as fs.appendFile() to append data to a file, fs.rename() to rename a file, and fs.unlink() to delete a file.

5. Practice Exercises

1. Write a Node.js script to create a new text file and write the string "I'm learning Node.js!" to it.
2. Write a Node.js script to read the file created in the previous exercise and log its contents to the console.
3. Modify the script from exercise 2 to append "And it's fun!" to the file before reading it.

Remember, practice is key to mastering any programming concept. Happy coding!