[core] Do not clear undefined timer IDs (#5002)

* Do not clear undefined timeouts

* Add test

* Changeset

* tweak tests

---------

Co-authored-by: Mateusz Burzyński <mateuszburzynski@gmail.com>

.changeset/lucky-horses-pay.md

@@ -0,0 +1,5 @@
+---
+'xstate': patch
+---
+
+Fix an issue where `clearTimeout(undefined)` was sometimes being called, which can cause errors for some clock implementations. See https://github.com/statelyai/xstate/issues/5001 for details.

packages/core/src/system.ts

@@ -139,7 +139,9 @@ export function createSystem<T extends ActorSystemInfo>(
  delete timerMap[scheduledEventId];
  delete system._snapshot._scheduledEvents[scheduledEventId];
 
- clock.clearTimeout(timeout);
+ if (timeout !== undefined) {
+ clock.clearTimeout(timeout);
+ }
  },
  cancelAll: (actorRef) => {
  for (const scheduledEventId in system._snapshot._scheduledEvents) {

packages/core/test/actions.test.ts

@@ -3384,7 +3384,7 @@ describe('raise', () => {
 });
 
 describe('cancel', () => {
- it('should be possible to cancel a raised delayed event', () => {
+ it('should be possible to cancel a raised delayed event', async () => {
  const machine = createMachine({
  initial: 'a',
  states: {
@@ -3405,11 +3405,18 @@ describe('cancel', () => {
 
  const actor = createActor(machine).start();
 
+ // This should raise the 'RAISED' event after 1ms
+ actor.send({ type: 'NEXT' });
+
+ // This should cancel the 'RAISED' event
  actor.send({ type: 'CANCEL' });
 
- setTimeout(() => {
- expect(actor.getSnapshot().value).toBe('a');
- }, 10);
+ await new Promise<void>((res) => {
+ setTimeout(() => {
+ expect(actor.getSnapshot().value).toBe('a');
+ res();
+ }, 10);
+ });
  });
 
  it('should cancel only the delayed event in the machine that scheduled it when canceling the event with the same ID in the machine that sent it first', async () => {
@@ -3507,6 +3514,31 @@ describe('cancel', () => {
  expect(fooSpy).toHaveBeenCalledTimes(1);
  expect(barSpy).not.toHaveBeenCalled();
  });
+
+ it('should not try to clear an undefined timeout when canceling an unscheduled timer', async () => {
+ const spy = jest.fn();
+
+ const machine = createMachine({
+ on: {
+ FOO: {
+ actions: cancel('foo')
+ }
+ }
+ });
+
+ const actorRef = createActor(machine, {
+ clock: {
+ setTimeout,
+ clearTimeout: spy
+ }
+ }).start();
+
+ actorRef.send({
+ type: 'FOO'
+ });
+
+ expect(spy.mock.calls.length).toBe(0);
+ });
 });
 
 describe('assign action order', () => {

packages/core/test/after.test.ts

@@ -1,4 +1,5 @@
-import { createMachine, createActor } from '../src/index.ts';
+import { sleep } from '@xstate-repo/jest-utils';
+import { createMachine, createActor, cancel } from '../src/index.ts';
 
 const lightMachine = createMachine({
  id: 'light',
@@ -43,6 +44,35 @@ describe('delayed transitions', () => {
  expect(actorRef.getSnapshot().value).toBe('yellow');
  });
 
+ it('should not try to clear an undefined timeout when exiting source state of a delayed transition', async () => {
+ // https://github.com/statelyai/xstate/issues/5001
+ const spy = jest.fn();
+
+ const machine = createMachine({
+ initial: 'green',
+ states: {
+ green: {
+ after: {
+ 1: 'yellow'
+ }
+ },
+ yellow: {}
+ }
+ });
+
+ const actorRef = createActor(machine, {
+ clock: {
+ setTimeout,
+ clearTimeout: spy
+ }
+ }).start();
+
+ // when the after transition gets executed it tries to clear its own timer when exiting its source state
+ await sleep(5);
+ expect(actorRef.getSnapshot().value).toBe('yellow');
+ expect(spy.mock.calls.length).toBe(0);
+ });
+
  it('should format transitions properly', () => {
  const greenNode = lightMachine.states.green;