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File System Module

The fs (File System) module in Node.js provides an API to interact with the file system, enabling you to read, write, update, and delete files and directories.

Illustration of File System Module
Illustration of File System Module

💡 Core Concept

The fs module is built-in and does not require installation. Use require('fs') to access its functions.

Importing the File System Module

📌 Deep Dive: Importing fs

JAVASCRIPT
const fs = require('fs');

Key Methods in the File System Module

Common fs Methods
MethodDescription
fs.readFile()Reads the contents of a file asynchronously.
fs.writeFile()Writes data to a file asynchronously, replacing the file if it exists.
fs.appendFile()Appends data to a file asynchronously, creating it if it doesn't exist.
fs.unlink()Deletes a file asynchronously.
fs.mkdir()Creates a new directory asynchronously.
fs.readdir()Reads the contents of a directory asynchronously.

Asynchronous vs Synchronous Methods

Most fs methods have both asynchronous and synchronous versions. Asynchronous methods accept callbacks and do not block the event loop. Synchronous methods block execution until complete and are named with the Sync suffix.

Comparison of Async and Sync Methods
Async MethodSync Method
fs.readFile(path, callback)fs.readFileSync(path)
fs.writeFile(path, data, callback)fs.writeFileSync(path, data)
fs.mkdir(path, callback)fs.mkdirSync(path)

⚠️ Use Async Methods Preferably

Synchronous fs methods block the Node.js event loop and can degrade performance. Use asynchronous methods in production code.

Essential Examples

📌 Deep Dive: Reading a File Asynchronously

JAVASCRIPT
fs.readFile('example.txt', 'utf8', (err, data) => {
  if (err) {
    console.error('Error reading file:', err);
    return;
  }
  console.log(data);
});
Output
Contents of example.txt printed to console

📌 Deep Dive: Writing to a File Asynchronously

JAVASCRIPT
const content = 'Hello, File System Module!';

fs.writeFile('output.txt', content, (err) => {
  if (err) {
    console.error('Error writing file:', err);
    return;
  }
  console.log('File written successfully.');
});
Output
File written successfully.

📌 Deep Dive: Creating a Directory

JAVASCRIPT
fs.mkdir('new_folder', { recursive: true }, (err) => {
  if (err) {
    console.error('Error creating directory:', err);
    return;
  }
  console.log('Directory created successfully.');
});
Output
Directory created successfully.

💡 Recursive Option in fs.mkdir()

Setting recursive: true ensures that nested directories are created if they don't exist, similar to mkdir -p in UNIX.

Reading Directory Contents

📌 Deep Dive: Listing Files in a Directory

JAVASCRIPT
fs.readdir('.', (err, files) => {
  if (err) {
    console.error('Error reading directory:', err);
    return;
  }
  console.log('Files in current directory:', files);
});
Output
Files in current directory: [ 'file1.js', 'file2.txt', 'new_folder', ... ]

⚠️ Error Handling

Always check the err parameter in callbacks to handle file system errors gracefully.

Summary

  • Import the fs module with require('fs').
  • Use asynchronous methods like fs.readFile and fs.writeFile to avoid blocking.
  • Use synchronous methods only for scripts or during startup when blocking is acceptable.
  • Handle errors in callbacks to avoid crashes.
  • Common tasks: reading, writing, appending files; creating directories; listing contents; deleting files.
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