events.addAbortListener(signal,listener) function in Node.js

The events.addAbortListener(signal, listener) in Node.js is relatively recent and intended to help the developer better handle signal-listener interactions. It can best be implemented on long-running asynchronous operations with the possibility to cancel or abort an operation or event depending on a signal, such as an AbortController signal.

Abort Signals in Node.js

Let's dig into the details of events.addAbortListener and get started with a general discussion about abort signals and how Node.js applies them. Abort signals are typically represented by an instance of the AbortSignal interface. It interface forms a part of the wider AbortController API, which defines a mechanism for aborting or cancelling asynchronous tasks or operations in JavaScript. AbortController can be applied in the context of both Node.js and a web browser.

An AbortController is the object that will generate an AbortSignal. You can create a signal that you can listen for abortion (i.e., cancellation) of a certain process. It is especially useful when you will want to cancel a fetch request, any long-running task, or even a stream operation if a certain condition becomes true.

Example of AbortController and AbortSignal

Here is a basic example demonstrating the use of an AbortController:

Output:

Explanation:

When the controller.abort() function is called, the abort event is emitted on the signal, and any listener that was registered to handle that event will get called. In this case, the listener just logs a message to the console.

Overview of events.addAbortListener

The events.addAbortListener(signal, listener) method should make adding an abort signal listener as simple as possible. It encapsulates the typical mechanism of emitting the event offered by Node.js with the ability AbortController and AbortSignal have to handle an abort signal. In this way, when the abort signal gets sent, the corresponding listener will automatically be executed.

Syntax:

The events.addAbortListener function has the following signature:

Parameters:

• Signal: This is an object in the AbortSignal. A signal that creates an AbortController API and can be expressed as a signal to the listener when it aborts.
• Listener: It is the function to be executed when an abort signal is issued. A listener function most of the times carries out cleanup procedures, cancels other running processes, or reports the operation being canceled to the other parts of the application.

Key Benefits

Simplified Abort Handling instead of manually attaching listeners on abort signals using the addEventListener method, you can use this function to directly link the abort signal with your listener.

• Cleaner Code: This approach reduces the boilerplate code often associated with handling abort events and improves readability.
• Automatic cleanup: Whenever a listener is activated, the functions such as the events.addAbortListener function ensure that the listener automatically cleans up and minimizes the occurrence of memory leaks.

Practical Usage of events.addAbortListener

The events.addAbortListener function is very useful when you are using long-running or asynchronous tasks that have to be cancelled or aborted in certain conditions.

Example 1: Cancelling a File Download Operation

If you are writing a downloader application from which, based on a download from the server, you need to be able to cancel the download if the user wants to. Using events.addAbortListener can handle the abort signal much more briefly and elegantly.

Output:

Explanation:

• In this example, we use the events.addAbortListener function to register a listener for the abort signal.
• If the user is attempting to trigger the abort action (in our test case, simulated through timeout), the listener gets called and the file stream gets closed.
• It terminates all subsequent writes to the file once it receives the abort signal.

Example 2: Cancelling a very long-running Computation

Another use case is aborting a long-running computation, like data processing, when it is no longer needed by the user.

Output: