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.

Lets 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

Heres 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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