Node.js File System (FS)

Node.js File System

In Node.js, file I/O operations are built upon simple wrappers around standard POSIX functions. The File System (fs) module in Node.js enables developers to work with files easily — from reading and writing to updating and deleting files.

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To use the File System module, you can import it using the following syntax:

var fs = require("fs");

Node.js FS – Reading a File

Every method in the fs module has both synchronous and asynchronous versions.

• Asynchronous methods take a callback function as the last parameter and do not block the event loop, allowing other code to execute while the file operation is in progress.
• Synchronous methods, on the other hand, block program execution until the operation completes.

The asynchronous approach is generally preferred for better performance and scalability.

Let’s look at an example.

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Create a text file named input.txt with the following content:

File: input.txt

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Now, create a JavaScript file named main.js with 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 code in the Node.js terminal using the command:

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node main.js

Node.js – Opening a File

You can open a file in asynchronous mode using the following syntax:

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

Parameters:

• path: The name or path of the file to be opened.
• flags: Specifies how the file should be opened (read, write, append, etc.).
• mode: Defines the file permissions (default is 0666, which allows read and write).
• callback: A function that receives two arguments — err and fd (file descriptor).

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Common File Open Flags

Here’s an example of opening a file asynchronously:

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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

You can get detailed information about a file using the fs.stat() method.

Syntax:

fs.stat(path, callback)

Parameters:

• path: The name or path of the file.
• callback: Function with two parameters — err and stats. The stats object is an instance of fs.Stats and provides various file properties and methods.

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Common fs.Stats Methods

Example:

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

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