AbortController

AbortController is a built-in object that produces a reusable signal you hand to async work, so calling its abort() method can cancel a fetch, timer, or any operation listening to that signal.

Learn AbortController in our free JavaScript course — an interactive lesson with runnable examples, a practice exercise and a quick reference.

Part of the free JavaScript course at LearnCodingFast — hands-on lessons with examples you run in your browser, plus practice exercises and a quick quiz.

It is how you stop work you no longer need: cancelling a stale search request, tearing down a fetch when a component unmounts, or enforcing a hard timeout.

📚 Prerequisites: You should know promises and async/await with try/catch, since aborting surfaces as a rejected promise.

🔔 Real-World Analogy: An AbortController is a fire alarm . The controller is the pull handle; the signal is the wiring that runs to every room. You give the signal to each async task ("listen for the alarm"). Pulling the handle ( abort() ) rings everywhere at once and every task that was listening stops what it is doing.

Create a controller with new AbortController() . It exposes a read-only signal that you pass to the operation you want to be able to cancel, and an abort() method that flips that signal to the aborted state. The signal has an aborted boolean and fires an "abort" event when triggered.

Pass signal to fetch and call abort() to cancel the request. The fetch promise rejects with an AbortError , which you catch and distinguish from a real network failure by checking err.name . This is the classic "cancel the previous search as the user types" pattern:

⚠️ Always check err.name : Treating an AbortError as a real error shows users scary "request failed" messages for something they (or your code) caused on purpose.

The runnable demo below uses a cancellable delay that listens to the signal — exactly the shape fetch follows — so you can watch an abort reject with an AbortError in Node:

Replace the blank with the method that cancels the controller so the event fires.

When you only need a deadline, skip the controller entirely. AbortSignal.timeout(ms) returns a signal that auto-aborts after ms milliseconds. There is also AbortSignal.any([...]) to abort as soon as any of several signals fires — handy for "cancel on either a timeout or the user clicking stop".

Replace the blank so the code checks for a deliberate abort instead of treating it as a real error.

Predict the output before revealing the answer.

true — abort() permanently flips the signal's aborted flag.

No — the signal stays aborted. Create a fresh new AbortController() for each new operation.

Start two waits. When the fast one finishes, abort the slow one so its cleanup runs. This mirrors cancelling a stale request once fresher data arrives.

Up next: Web Workers — run heavy work off the main thread. 🧵

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