Node.js Writable Stream unpipe Event

Last Updated : 28 Apr, 2025

The 'unpipe' event in a Writable Stream is emitted when the stream.unpipe() method is being called on a Readable stream by detaching this Writable from its set of destinations. 

Syntax:

 Event: 'unpipe'

Return Value: If the unpipe() method is being called then this event is emitted else it's not emitted. 

The below examples illustrate the use of the 'unpipe' event in Node.js: 

Example 1: 

javascript 
// Node.js program to demonstrate the    
// unpipe event

// Accessing fs module
const fs = require("fs");

// Create a readable stream
const readable = fs.createReadStream('input.txt');

// Create a writable stream
const writable = fs.createWriteStream('output.txt');

// Handling unpipe event
writable.on("unpipe", readable => {
    console.log("Unpiped!");
});

// Calling pipe method
readable.pipe(writable);

// Calling unpipe method
readable.unpipe(writable);

console.log("Program Ended...");

Output:

Unpiped!
Program Ended...

Example 2: 

javascript 
// Node.js program to demonstrate the    
// unpipe event

// Accessing fs module
const fs = require("fs");

// Create a readable stream
const readable = fs.createReadStream('input.txt');

// Create a writable stream
const writable = fs.createWriteStream('output.txt');

// Handling unpipe event
writable.on("unpipe", readable => {
    console.log("Unpiped!");
});

console.log("Program Ended...")

Output:

Program Ended...

So, here unpipe() function is not called so the unpipe event is not emitted. 

Reference: https://nodejs.org/api/stream.html#stream_event_unpipe

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