Linked controllers

EnhancedAbortController.createLinkedController(...signals) is .NET’s CreateLinkedTokenSource. The new controller aborts as soon as any of the signals aborts, with that signal’s reason. linkSignals is an alias.

{
  // Stops when the request aborts, or after 2 s, whichever comes first.
  using 
using step: EnhancedAbortController
step = 
class EnhancedAbortController
An AbortController with .NET CancellationTokenSource features. It is an AbortController,
and controller.signal is a real AbortSignal: pass it to fetch, AbortSignal.any, streams,
timers and any other API that takes a signal.
@example 
const controller = new EnhancedAbortController().abortAfter(TimeSpan.fromSeconds(5));
const response = await fetch(url, { signal: controller.signal });
EnhancedAbortController.
EnhancedAbortController.createLinkedController<EnhancedAbortController>(this: new () => EnhancedAbortController, ...signals: Array<AbortSignal | null | undefined>): EnhancedAbortController
A controller that aborts as soon as any of signals aborts, with that signal's reason, like .NET's
CreateLinkedTokenSource. Aborting the linked controller does not affect the parents. Its listeners
on the parents are removed when it aborts or is disposed, so short-lived links on a long-lived parent
don't leak. undefined/null entries (optional signals) and EnhancedAbortSignal.none are skipped.
createLinkedController(
const request: {
    signal: AbortSignal;
}
request.
signal: AbortSignal
signal).
EnhancedAbortController.abortAfter(delay: Delay): EnhancedAbortController
Aborts after delay, like .NET's CancelAfter: calling it again replaces the previous schedule,
and Infinity / -1 / TimeSpan.infinite cancel it. The reason is a DOMException named
TimeoutError, as with AbortSignal.timeout. The timer never keeps the process alive, and delays
longer than 24.8 days work. Does nothing once aborted. Returns the controller, for chaining.
@throws ― RangeError for NaN, negative (other than -1) or non-numeric delays.
@throws ― Error if the controller was disposed.
abortAfter(2000);
  await 
function queryOrders(signal: AbortSignal): Promise<void>
queryOrders(
using step: EnhancedAbortController
step.
EnhancedAbortController.signal: EnhancedSignal
The controller's signal: a real AbortSignal, always the same object.
signal);
}

Try it

A request signal with three steps, each linked to it with its own deadline. Let a step time out, abort the parent, dispose a step, or create 1000 short-lived children, and watch the listener count on the parent.

The rules

Reason forwarding. When a parent aborts, the child aborts with the parent’s reason, the same object. A child that times out on its own has a TimeoutError.
One way. Aborting or disposing the child never touches the parents.
Already aborted parent. Linking to a signal that has already aborted gives a child that is aborted at once, with that reason.
Clean-up. The child puts one listener on each parent. All of them are removed when the child aborts (for any reason, including one parent aborting) or is disposed. Short-lived children on a long-lived parent leave nothing behind.
Optional signals. undefined and null entries are skipped, and so is EnhancedAbortSignal.none, so you can pass an optional caller signal straight in. With no signals left, the child is just a fresh controller.
Subclasses. Called on a subclass, createLinkedController and timeout return an instance of that subclass.

const 
const parent: AbortController
parent = new 
var AbortController: new () => AbortController
The AbortController interface represents a controller object that allows you to abort one or more Web requests as and when desired.
MDN Reference
AbortController();
const 
const child: EnhancedAbortController
child = 
class EnhancedAbortController
An AbortController with .NET CancellationTokenSource features. It is an AbortController,
and controller.signal is a real AbortSignal: pass it to fetch, AbortSignal.any, streams,
timers and any other API that takes a signal.
@example 
const controller = new EnhancedAbortController().abortAfter(TimeSpan.fromSeconds(5));
const response = await fetch(url, { signal: controller.signal });
EnhancedAbortController.
EnhancedAbortController.createLinkedController<EnhancedAbortController>(this: new () => EnhancedAbortController, ...signals: Array<AbortSignal | null | undefined>): EnhancedAbortController
A controller that aborts as soon as any of signals aborts, with that signal's reason, like .NET's
CreateLinkedTokenSource. Aborting the linked controller does not affect the parents. Its listeners
on the parents are removed when it aborts or is disposed, so short-lived links on a long-lived parent
don't leak. undefined/null entries (optional signals) and EnhancedAbortSignal.none are skipped.
createLinkedController(
const parent: AbortController
parent.
AbortController.signal: AbortSignal
The signal read-only property of the AbortController interface returns an AbortSignal object instance, which can be used to communicate with/abort an asynchronous operation as desired.
MDN Reference
signal);

const parent: AbortController
parent.
AbortController.abort(reason?: any): void
The abort() method of the AbortController interface aborts an asynchronous operation before it has completed.
MDN Reference
abort(new 
var Error: ErrorConstructor
new (message?: string, options?: ErrorOptions) => Error (+1 overload)
Error('client disconnected'));
const child: EnhancedAbortController
child.
EnhancedAbortController.reason: unknown
Same as signal.reason: why it aborted, undefined until then.
reason === 
const parent: AbortController
parent.
AbortController.signal: AbortSignal
The signal read-only property of the AbortController interface returns an AbortSignal object instance, which can be used to communicate with/abort an asynchronous operation as desired.
MDN Reference
signal.
AbortSignal.reason: any
The reason read-only property returns a JavaScript value that indicates the abort reason.
MDN Reference
reason; // true

async function 
function load(id: string, signal?: AbortSignal): Promise<Response>
load(
id: string
id: string, 
signal: AbortSignal | undefined
signal?: 
interface AbortSignal
The AbortSignal interface represents a signal object that allows you to communicate with an asynchronous operation (such as a fetch request) and abort it if required via an AbortController object.
MDN Reference
AbortSignal) {
  using 
using local: EnhancedAbortController
local = 
class EnhancedAbortController
An AbortController with .NET CancellationTokenSource features. It is an AbortController,
and controller.signal is a real AbortSignal: pass it to fetch, AbortSignal.any, streams,
timers and any other API that takes a signal.
@example 
const controller = new EnhancedAbortController().abortAfter(TimeSpan.fromSeconds(5));
const response = await fetch(url, { signal: controller.signal });
EnhancedAbortController.
EnhancedAbortController.createLinkedController<EnhancedAbortController>(this: new () => EnhancedAbortController, ...signals: Array<AbortSignal | null | undefined>): EnhancedAbortController
A controller that aborts as soon as any of signals aborts, with that signal's reason, like .NET's
CreateLinkedTokenSource. Aborting the linked controller does not affect the parents. Its listeners
on the parents are removed when it aborts or is disposed, so short-lived links on a long-lived parent
don't leak. undefined/null entries (optional signals) and EnhancedAbortSignal.none are skipped.
createLinkedController(
signal: AbortSignal | undefined
signal).
EnhancedAbortController.abortAfter(delay: Delay): EnhancedAbortController
Aborts after delay, like .NET's CancelAfter: calling it again replaces the previous schedule,
and Infinity / -1 / TimeSpan.infinite cancel it. The reason is a DOMException named
TimeoutError, as with AbortSignal.timeout. The timer never keeps the process alive, and delays
longer than 24.8 days work. Does nothing once aborted. Returns the controller, for chaining.
@throws ― RangeError for NaN, negative (other than -1) or non-numeric delays.
@throws ― Error if the controller was disposed.
abortAfter(5000); // signal may be undefined
  return await 
function fetch(input: string | URL | Request, init?: RequestInit): Promise<Response> (+1 overload)
MDN Reference
fetch(`/items/${
id: string
id}`, { 
RequestInit.signal?: AbortSignal | null | undefined
An AbortSignal to set request's signal.
signal: 
using local: EnhancedAbortController
local.
EnhancedAbortController.signal: EnhancedSignal
The controller's signal: a real AbortSignal, always the same object.
signal }); // await: dispose only after the fetch settles
}

createLinkedController or AbortSignal.any?

Both forward the first reason. Pick by what you need:

	`createLinkedController`	`AbortSignal.any` / `EnhancedAbortSignal.any`
Result	A controller: you can `abort()` it and give it `abortAfter`	A signal only
Parent listeners released	When it aborts or is disposed: deterministic	When the combined signal is garbage-collected
Optional entries	Skipped	`EnhancedAbortSignal.any` skips them; native `AbortSignal.any` throws

EnhancedAbortSignal.any delegates to native AbortSignal.any, so use it when you just need one signal from several.