Node.js File System (fs) Module

Node.js File System

In Node.js, file input and output operations are handled using the built-in File System (fs) module. It provides a simple way to work with files and directories, including reading, writing, opening, updating, and deleting files.

The File System module can be imported using the following syntax:

var fs = require("fs");

Node.js FS Reading a File

Methods in the Node.js fs module are available in both synchronous and asynchronous forms.

• Asynchronous methods: These methods use a callback and allow other operations to continue while the file operation is in progress. They do not block the Node.js event loop.
• Synchronous methods: These methods block program execution until the file operation has completed.

Asynchronous file operations are generally preferred in server-side applications because they provide better performance and scalability.

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Example: Reading a File in Node.js

First, create a text file named input.txt and add the following content:

File: input.txt

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Now create a JavaScript file named main.js and add the following code:

File: main.js

var fs = require("fs");

// Asynchronous read
fs.readFile('input.txt', function (err, data) {
   if (err) {
       return console.error(err);
   }
   console.log("Asynchronous read: " + data.toString());
});

// Synchronous read
var data = fs.readFileSync('input.txt');
console.log("Synchronous read: " + data.toString());

console.log("Program Ended");

Run the program from the Node.js terminal using:

node main.js

Node.js Opening a File

The fs.open() method can be used to open a file asynchronously.

Syntax:

fs.open(path, flags[, mode], callback)

Parameters of fs.open()

• path: Specifies the name or path of the file.
• flags: Specifies how the file should be opened, such as for reading, writing, or appending.
• mode: Defines file permissions. The default value is 0666.
• callback: A function that receives err and fd, where fd is the file descriptor.

Common File Open Flags

Example: Opening a File Asynchronously

File: main.js

var fs = require("fs");

console.log("Going to open file!");

fs.open('input.txt', 'r+', function(err, fd) {
   if (err) {
       return console.error(err);
   }

   console.log("File opened successfully!");
});

Run the program using:

node main.js

Node.js File Information

The fs.stat() method can be used to retrieve detailed information about a file or directory.

Syntax:

fs.stat(path, callback)

Parameters of fs.stat()

• path: Specifies the name or path of the file.
• callback: A function that receives err and stats. The stats object is an instance of fs.Stats and provides information about the file.

Common fs.Stats Methods

Example: Getting File Information

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File: main.js

var fs = require("fs");

console.log("Going to get file info!");

fs.stat('input.txt', function (err, stats) {
   if (err) {
       return console.error(err);
   }

   console.log(stats);
   console.log("Got file info successfully!");
   console.log("isFile ? " + stats.isFile());
   console.log("isDirectory ? " + stats.isDirectory());
});

Run the script using:

node main.js

Conclusion

The Node.js fs module provides essential functionality for working with files and directories. Using methods such as readFile(), readFileSync(), open(), and stat(), developers can efficiently read files, open file descriptors, and retrieve file information in Node.js applications.

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