Abortable Promise

Native promises can't be cancelled. Build AbortablePromise, a Promise subclass whose work can be stopped from outside.

const p = new AbortablePromise((resolve, reject, onAbort) => {
  const id = setTimeout(() => resolve("done"), 1000);
  onAbort(() => clearTimeout(id));   // how to stop the work
});
p.abort();                           // runs the cleanup, rejects p with an AbortError

Rules

• The executor receives a third argument, onAbort(cleanup), which registers the function that stops the work.
• p.abort(reason?) on a pending promise runs the cleanup, if one was registered, and rejects p with reason — by default an Error whose name is "AbortError".
• Once p has settled — resolved, rejected, or already aborted — abort() does nothing: no cleanup, no change of outcome.
• Everything else behaves like a native promise: a throwing executor rejects, then and catch chain, and p instanceof Promise holds.

The grader stubs setTimeout and clearTimeout with a virtual clock and records what your callbacks see, in order.