Node.js fs.createWriteStream() Method

The fs.createWriteStream() method in Node.js is used to create a writable stream for writing data to a file. This method is part of the fs (file system) module and is ideal for writing large amounts of data to a file in chunks rather than loading the entire content into memory at once. It is particularly useful for tasks like logging, file uploads, and generating large files.

fs.createWriteStream() Method

The createWriteStream() method is an inbuilt application programming interface of fs module which allows to quickly make a writable stream for the purpose of writing data to a file. This method may be a smarter option compared to methods like fs.writeFile when it comes to very large amounts of data.

Syntax:

fs.createWriteStream( path, options )

Parameters: This method accept two parameters as mentioned above and described below:

• path: The path to the file where you want to write the data. If the file does not exist, it will be created.
• options: An optional parameter that allows you to specify options such as encoding, flags, and mode.

Return Value: This method returns the fs.writeStream object.

Features

• Efficient Memory Usage: The stream writes data in chunks, making it memory-efficient, especially when dealing with large files.
• Asynchronous: Writing operations are non-blocking, allowing the application to continue processing other tasks while data is being written.
• Pipeable: Writable streams can be piped to other readable streams, enabling powerful data transformation and transfer operations.

Following example illustrates the createWriteStream() method in Node.js:

Example 1: This example uses fs.createWriteStream() method to write some content into the file.

// Node.js program to demonstrate the 
// fs.createWriteStream() method 

// Include fs module 
let fs = require('fs'), 

// Use fs.createWriteStream() method 
// to write the file 
let writer = fs.createWriteStream('test_gfg.txt') 

// Read and display the file data on console 
writer.write('GeeksforGeeks');

Output:

test_gfg.txt file data:
GeeksforGeeks

Example 2:  Piping from readable streams.

// Node.js program to demonstrate the  
// fs.createWriteStream() method 

// Include fs module 
let fs = require('fs');
 
let writer = fs.createWriteStream('test_gfg.txt', {
        flags: 'w'
    });
 
// Use fs.createReadStream() method 
// to read the file 
let reader = fs.createReadStream('test_gfg.txt')
         .pipe(writer);

With writable streams such as the streams created with fs.createWriteStream, data can be piped from a readable stream.

Summary

The fs.createWriteStream() method in Node.js is a versatile and efficient way to write data to files, especially when working with large amounts of data. Its ability to handle data in chunks, combined with non-blocking I/O, makes it a powerful tool for building scalable and high-performance Node.js applications. Whether you’re logging information, generating files, or handling file uploads, fs.createWriteStream() provides the functionality you need to write data efficiently and effectively.