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Make Scheduler.postTask generic over the callback result #2583

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Merged
github-actions merged 1 commit into from
Nov 8, 2026
+112 −48
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Make Scheduler.postTask generic over the callback result #2583

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6 changes: 3 additions & 3 deletions baselines/dom.generated.d.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -35284,7 +35284,7 @@ interface Scheduler {
*
* [MDN Reference](https://developer.mozilla.org/docs/Web/API/Scheduler/postTask)
*/
postTask(callback: SchedulerPostTaskCallback, options?: SchedulerPostTaskOptions): Promise<any>;
postTask<T = any>(callback: SchedulerPostTaskCallback<T>, options?: SchedulerPostTaskOptions): Promise<T>;
/**
* The **`yield()`** method of the Scheduler interface is used for yielding to the main thread during a task and continuing execution later, with the continuation scheduled as a prioritized task (see the Prioritized Task Scheduling API for more information). This allows long-running work to be broken up so the browser stays responsive.
*
Expand Down Expand Up @@ -43919,8 +43919,8 @@ interface ResizeObserverCallback {
(entries: ResizeObserverEntry[], observer: ResizeObserver): void;
}

interface SchedulerPostTaskCallback {
(): any;
interface SchedulerPostTaskCallback<T = any> {
(): T | PromiseLike<T>;
}

interface TransformerFlushCallback<O> {
Expand Down
6 changes: 3 additions & 3 deletions baselines/serviceworker.generated.d.ts
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Expand Up @@ -8558,7 +8558,7 @@ interface Scheduler {
*
* [MDN Reference](https://developer.mozilla.org/docs/Web/API/Scheduler/postTask)
*/
postTask(callback: SchedulerPostTaskCallback, options?: SchedulerPostTaskOptions): Promise<any>;
postTask<T = any>(callback: SchedulerPostTaskCallback<T>, options?: SchedulerPostTaskOptions): Promise<T>;
/**
* The **`yield()`** method of the Scheduler interface is used for yielding to the main thread during a task and continuing execution later, with the continuation scheduled as a prioritized task (see the Prioritized Task Scheduling API for more information). This allows long-running work to be broken up so the browser stays responsive.
*
Expand Down Expand Up @@ -13349,8 +13349,8 @@ interface ReportingObserverCallback {
(reports: Report[], observer: ReportingObserver): void;
}

interface SchedulerPostTaskCallback {
(): any;
interface SchedulerPostTaskCallback<T = any> {
(): T | PromiseLike<T>;
}

interface TransformerFlushCallback<O> {
Expand Down
6 changes: 3 additions & 3 deletions baselines/sharedworker.generated.d.ts
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Expand Up @@ -8141,7 +8141,7 @@ interface Scheduler {
*
* [MDN Reference](https://developer.mozilla.org/docs/Web/API/Scheduler/postTask)
*/
postTask(callback: SchedulerPostTaskCallback, options?: SchedulerPostTaskOptions): Promise<any>;
postTask<T = any>(callback: SchedulerPostTaskCallback<T>, options?: SchedulerPostTaskOptions): Promise<T>;
/**
* The **`yield()`** method of the Scheduler interface is used for yielding to the main thread during a task and continuing execution later, with the continuation scheduled as a prioritized task (see the Prioritized Task Scheduling API for more information). This allows long-running work to be broken up so the browser stays responsive.
*
Expand Down Expand Up @@ -13075,8 +13075,8 @@ interface ReportingObserverCallback {
(reports: Report[], observer: ReportingObserver): void;
}

interface SchedulerPostTaskCallback {
(): any;
interface SchedulerPostTaskCallback<T = any> {
(): T | PromiseLike<T>;
}

interface TransformerFlushCallback<O> {
Expand Down
6 changes: 3 additions & 3 deletions baselines/ts5.5/dom.generated.d.ts
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Expand Up @@ -35259,7 +35259,7 @@ interface Scheduler {
*
* [MDN Reference](https://developer.mozilla.org/docs/Web/API/Scheduler/postTask)
*/
postTask(callback: SchedulerPostTaskCallback, options?: SchedulerPostTaskOptions): Promise<any>;
postTask<T = any>(callback: SchedulerPostTaskCallback<T>, options?: SchedulerPostTaskOptions): Promise<T>;
/**
* The **`yield()`** method of the Scheduler interface is used for yielding to the main thread during a task and continuing execution later, with the continuation scheduled as a prioritized task (see the Prioritized Task Scheduling API for more information). This allows long-running work to be broken up so the browser stays responsive.
*
Expand Down Expand Up @@ -43893,8 +43893,8 @@ interface ResizeObserverCallback {
(entries: ResizeObserverEntry[], observer: ResizeObserver): void;
}

interface SchedulerPostTaskCallback {
(): any;
interface SchedulerPostTaskCallback<T = any> {
(): T | PromiseLike<T>;
}

interface TransformerFlushCallback<O> {
Expand Down
6 changes: 3 additions & 3 deletions baselines/ts5.5/serviceworker.generated.d.ts
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Expand Up @@ -8555,7 +8555,7 @@ interface Scheduler {
*
* [MDN Reference](https://developer.mozilla.org/docs/Web/API/Scheduler/postTask)
*/
postTask(callback: SchedulerPostTaskCallback, options?: SchedulerPostTaskOptions): Promise<any>;
postTask<T = any>(callback: SchedulerPostTaskCallback<T>, options?: SchedulerPostTaskOptions): Promise<T>;
/**
* The **`yield()`** method of the Scheduler interface is used for yielding to the main thread during a task and continuing execution later, with the continuation scheduled as a prioritized task (see the Prioritized Task Scheduling API for more information). This allows long-running work to be broken up so the browser stays responsive.
*
Expand Down Expand Up @@ -13346,8 +13346,8 @@ interface ReportingObserverCallback {
(reports: Report[], observer: ReportingObserver): void;
}

interface SchedulerPostTaskCallback {
(): any;
interface SchedulerPostTaskCallback<T = any> {
(): T | PromiseLike<T>;
}

interface TransformerFlushCallback<O> {
Expand Down
6 changes: 3 additions & 3 deletions baselines/ts5.5/sharedworker.generated.d.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -8138,7 +8138,7 @@ interface Scheduler {
*
* [MDN Reference](https://developer.mozilla.org/docs/Web/API/Scheduler/postTask)
*/
postTask(callback: SchedulerPostTaskCallback, options?: SchedulerPostTaskOptions): Promise<any>;
postTask<T = any>(callback: SchedulerPostTaskCallback<T>, options?: SchedulerPostTaskOptions): Promise<T>;
/**
* The **`yield()`** method of the Scheduler interface is used for yielding to the main thread during a task and continuing execution later, with the continuation scheduled as a prioritized task (see the Prioritized Task Scheduling API for more information). This allows long-running work to be broken up so the browser stays responsive.
*
Expand Down Expand Up @@ -13072,8 +13072,8 @@ interface ReportingObserverCallback {
(reports: Report[], observer: ReportingObserver): void;
}

interface SchedulerPostTaskCallback {
(): any;
interface SchedulerPostTaskCallback<T = any> {
(): T | PromiseLike<T>;
}

interface TransformerFlushCallback<O> {
Expand Down
6 changes: 3 additions & 3 deletions baselines/ts5.5/webworker.generated.d.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -9706,7 +9706,7 @@ interface Scheduler {
*
* [MDN Reference](https://developer.mozilla.org/docs/Web/API/Scheduler/postTask)
*/
postTask(callback: SchedulerPostTaskCallback, options?: SchedulerPostTaskOptions): Promise<any>;
postTask<T = any>(callback: SchedulerPostTaskCallback<T>, options?: SchedulerPostTaskOptions): Promise<T>;
/**
* The **`yield()`** method of the Scheduler interface is used for yielding to the main thread during a task and continuing execution later, with the continuation scheduled as a prioritized task (see the Prioritized Task Scheduling API for more information). This allows long-running work to be broken up so the browser stays responsive.
*
Expand Down Expand Up @@ -15172,8 +15172,8 @@ interface ReportingObserverCallback {
(reports: Report[], observer: ReportingObserver): void;
}

interface SchedulerPostTaskCallback {
(): any;
interface SchedulerPostTaskCallback<T = any> {
(): T | PromiseLike<T>;
}

interface TransformerFlushCallback<O> {
Expand Down
6 changes: 3 additions & 3 deletions baselines/ts5.6/dom.generated.d.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -35281,7 +35281,7 @@ interface Scheduler {
*
* [MDN Reference](https://developer.mozilla.org/docs/Web/API/Scheduler/postTask)
*/
postTask(callback: SchedulerPostTaskCallback, options?: SchedulerPostTaskOptions): Promise<any>;
postTask<T = any>(callback: SchedulerPostTaskCallback<T>, options?: SchedulerPostTaskOptions): Promise<T>;
/**
* The **`yield()`** method of the Scheduler interface is used for yielding to the main thread during a task and continuing execution later, with the continuation scheduled as a prioritized task (see the Prioritized Task Scheduling API for more information). This allows long-running work to be broken up so the browser stays responsive.
*
Expand Down Expand Up @@ -43916,8 +43916,8 @@ interface ResizeObserverCallback {
(entries: ResizeObserverEntry[], observer: ResizeObserver): void;
}

interface SchedulerPostTaskCallback {
(): any;
interface SchedulerPostTaskCallback<T = any> {
(): T | PromiseLike<T>;
}

interface TransformerFlushCallback<O> {
Expand Down
6 changes: 3 additions & 3 deletions baselines/ts5.6/serviceworker.generated.d.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -8555,7 +8555,7 @@ interface Scheduler {
*
* [MDN Reference](https://developer.mozilla.org/docs/Web/API/Scheduler/postTask)
*/
postTask(callback: SchedulerPostTaskCallback, options?: SchedulerPostTaskOptions): Promise<any>;
postTask<T = any>(callback: SchedulerPostTaskCallback<T>, options?: SchedulerPostTaskOptions): Promise<T>;
/**
* The **`yield()`** method of the Scheduler interface is used for yielding to the main thread during a task and continuing execution later, with the continuation scheduled as a prioritized task (see the Prioritized Task Scheduling API for more information). This allows long-running work to be broken up so the browser stays responsive.
*
Expand Down Expand Up @@ -13346,8 +13346,8 @@ interface ReportingObserverCallback {
(reports: Report[], observer: ReportingObserver): void;
}

interface SchedulerPostTaskCallback {
(): any;
interface SchedulerPostTaskCallback<T = any> {
(): T | PromiseLike<T>;
}

interface TransformerFlushCallback<O> {
Expand Down
6 changes: 3 additions & 3 deletions baselines/ts5.6/sharedworker.generated.d.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -8138,7 +8138,7 @@ interface Scheduler {
*
* [MDN Reference](https://developer.mozilla.org/docs/Web/API/Scheduler/postTask)
*/
postTask(callback: SchedulerPostTaskCallback, options?: SchedulerPostTaskOptions): Promise<any>;
postTask<T = any>(callback: SchedulerPostTaskCallback<T>, options?: SchedulerPostTaskOptions): Promise<T>;
/**
* The **`yield()`** method of the Scheduler interface is used for yielding to the main thread during a task and continuing execution later, with the continuation scheduled as a prioritized task (see the Prioritized Task Scheduling API for more information). This allows long-running work to be broken up so the browser stays responsive.
*
Expand Down Expand Up @@ -13072,8 +13072,8 @@ interface ReportingObserverCallback {
(reports: Report[], observer: ReportingObserver): void;
}

interface SchedulerPostTaskCallback {
(): any;
interface SchedulerPostTaskCallback<T = any> {
(): T | PromiseLike<T>;
}

interface TransformerFlushCallback<O> {
Expand Down
6 changes: 3 additions & 3 deletions baselines/ts5.6/webworker.generated.d.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -9706,7 +9706,7 @@ interface Scheduler {
*
* [MDN Reference](https://developer.mozilla.org/docs/Web/API/Scheduler/postTask)
*/
postTask(callback: SchedulerPostTaskCallback, options?: SchedulerPostTaskOptions): Promise<any>;
postTask<T = any>(callback: SchedulerPostTaskCallback<T>, options?: SchedulerPostTaskOptions): Promise<T>;
/**
* The **`yield()`** method of the Scheduler interface is used for yielding to the main thread during a task and continuing execution later, with the continuation scheduled as a prioritized task (see the Prioritized Task Scheduling API for more information). This allows long-running work to be broken up so the browser stays responsive.
*
Expand Down Expand Up @@ -15172,8 +15172,8 @@ interface ReportingObserverCallback {
(reports: Report[], observer: ReportingObserver): void;
}

interface SchedulerPostTaskCallback {
(): any;
interface SchedulerPostTaskCallback<T = any> {
(): T | PromiseLike<T>;
}

interface TransformerFlushCallback<O> {
Expand Down
6 changes: 3 additions & 3 deletions baselines/ts5.9/dom.generated.d.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -35281,7 +35281,7 @@ interface Scheduler {
*
* [MDN Reference](https://developer.mozilla.org/docs/Web/API/Scheduler/postTask)
*/
postTask(callback: SchedulerPostTaskCallback, options?: SchedulerPostTaskOptions): Promise<any>;
postTask<T = any>(callback: SchedulerPostTaskCallback<T>, options?: SchedulerPostTaskOptions): Promise<T>;
/**
* The **`yield()`** method of the Scheduler interface is used for yielding to the main thread during a task and continuing execution later, with the continuation scheduled as a prioritized task (see the Prioritized Task Scheduling API for more information). This allows long-running work to be broken up so the browser stays responsive.
*
Expand Down Expand Up @@ -43916,8 +43916,8 @@ interface ResizeObserverCallback {
(entries: ResizeObserverEntry[], observer: ResizeObserver): void;
}

interface SchedulerPostTaskCallback {
(): any;
interface SchedulerPostTaskCallback<T = any> {
(): T | PromiseLike<T>;
}

interface TransformerFlushCallback<O> {
Expand Down
6 changes: 3 additions & 3 deletions baselines/ts5.9/serviceworker.generated.d.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -8555,7 +8555,7 @@ interface Scheduler {
*
* [MDN Reference](https://developer.mozilla.org/docs/Web/API/Scheduler/postTask)
*/
postTask(callback: SchedulerPostTaskCallback, options?: SchedulerPostTaskOptions): Promise<any>;
postTask<T = any>(callback: SchedulerPostTaskCallback<T>, options?: SchedulerPostTaskOptions): Promise<T>;
/**
* The **`yield()`** method of the Scheduler interface is used for yielding to the main thread during a task and continuing execution later, with the continuation scheduled as a prioritized task (see the Prioritized Task Scheduling API for more information). This allows long-running work to be broken up so the browser stays responsive.
*
Expand Down Expand Up @@ -13346,8 +13346,8 @@ interface ReportingObserverCallback {
(reports: Report[], observer: ReportingObserver): void;
}

interface SchedulerPostTaskCallback {
(): any;
interface SchedulerPostTaskCallback<T = any> {
(): T | PromiseLike<T>;
}

interface TransformerFlushCallback<O> {
Expand Down
6 changes: 3 additions & 3 deletions baselines/ts5.9/sharedworker.generated.d.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -8138,7 +8138,7 @@ interface Scheduler {
*
* [MDN Reference](https://developer.mozilla.org/docs/Web/API/Scheduler/postTask)
*/
postTask(callback: SchedulerPostTaskCallback, options?: SchedulerPostTaskOptions): Promise<any>;
postTask<T = any>(callback: SchedulerPostTaskCallback<T>, options?: SchedulerPostTaskOptions): Promise<T>;
/**
* The **`yield()`** method of the Scheduler interface is used for yielding to the main thread during a task and continuing execution later, with the continuation scheduled as a prioritized task (see the Prioritized Task Scheduling API for more information). This allows long-running work to be broken up so the browser stays responsive.
*
Expand Down Expand Up @@ -13072,8 +13072,8 @@ interface ReportingObserverCallback {
(reports: Report[], observer: ReportingObserver): void;
}

interface SchedulerPostTaskCallback {
(): any;
interface SchedulerPostTaskCallback<T = any> {
(): T | PromiseLike<T>;
}

interface TransformerFlushCallback<O> {
Expand Down
6 changes: 3 additions & 3 deletions baselines/ts5.9/webworker.generated.d.ts
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Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -9706,7 +9706,7 @@ interface Scheduler {
*
* [MDN Reference](https://developer.mozilla.org/docs/Web/API/Scheduler/postTask)
*/
postTask(callback: SchedulerPostTaskCallback, options?: SchedulerPostTaskOptions): Promise<any>;
postTask<T = any>(callback: SchedulerPostTaskCallback<T>, options?: SchedulerPostTaskOptions): Promise<T>;
/**
* The **`yield()`** method of the Scheduler interface is used for yielding to the main thread during a task and continuing execution later, with the continuation scheduled as a prioritized task (see the Prioritized Task Scheduling API for more information). This allows long-running work to be broken up so the browser stays responsive.
*
Expand Down Expand Up @@ -15172,8 +15172,8 @@ interface ReportingObserverCallback {
(reports: Report[], observer: ReportingObserver): void;
}

interface SchedulerPostTaskCallback {
(): any;
interface SchedulerPostTaskCallback<T = any> {
(): T | PromiseLike<T>;
}

interface TransformerFlushCallback<O> {
Expand Down
6 changes: 3 additions & 3 deletions baselines/webworker.generated.d.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -9709,7 +9709,7 @@ interface Scheduler {
*
* [MDN Reference](https://developer.mozilla.org/docs/Web/API/Scheduler/postTask)
*/
postTask(callback: SchedulerPostTaskCallback, options?: SchedulerPostTaskOptions): Promise<any>;
postTask<T = any>(callback: SchedulerPostTaskCallback<T>, options?: SchedulerPostTaskOptions): Promise<T>;
/**
* The **`yield()`** method of the Scheduler interface is used for yielding to the main thread during a task and continuing execution later, with the continuation scheduled as a prioritized task (see the Prioritized Task Scheduling API for more information). This allows long-running work to be broken up so the browser stays responsive.
*
Expand Down Expand Up @@ -15175,8 +15175,8 @@ interface ReportingObserverCallback {
(reports: Report[], observer: ReportingObserver): void;
}

interface SchedulerPostTaskCallback {
(): any;
interface SchedulerPostTaskCallback<T = any> {
(): T | PromiseLike<T>;
}

interface TransformerFlushCallback<O> {
Expand Down
38 changes: 38 additions & 0 deletions inputfiles/overridingTypes.jsonc
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Expand Up @@ -124,6 +124,19 @@
}
}
},
"SchedulerPostTaskCallback": {
"typeParameters": [
{
"name": "T",
"default": "any"
}
],
"signature": {
"0": {
"overrideType": "T | PromiseLike<T>"
}
}
},
"UnderlyingSourceStartCallback": {
"typeParameters": [
{
Expand Down Expand Up @@ -1891,6 +1904,31 @@
]
}
},
"Scheduler": {
"methods": {
"method": {
"postTask": {
"signature": {
"0": {
"typeParameters": [
{
"name": "T",
"default": "any"
}
],
"param": [
{
"name": "callback",
"overrideType": "SchedulerPostTaskCallback<T>"
}
],
"overrideType": "Promise<T>"
}
}
}
}
}
},
"MessagePort": {
"methods": {
"method": {
Expand Down
26 changes: 26 additions & 0 deletions unittests/files/schedulerPostTask.ts
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@@ -0,0 +1,26 @@
function assertType<T>(_x: T) {}

type Equals<A, B> =
(<T>() => T extends A ? 1 : 2) extends <T>() => T extends B ? 1 : 2
? true
: false;
declare function assertExact<T extends true>(): void;

@saschanaz Kagami Sascha Rosylight (saschanaz) Nov 8, 2026

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There are variations of this already in other tests, we should have a shared definition...

@MartinFerret Martin Ferret (MartinFerret) Nov 8, 2026

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You're right about the shared definition. I'd be happy to follow up with a PR going that way, are you OK with that?


async function testSchedulerPostTask() {
const num = await scheduler.postTask(() => 42);
assertExact<Equals<typeof num, number>>();

const str = await scheduler.postTask(async () => "done", {
priority: "background",
});
assertExact<Equals<typeof str, string>>();

const nothing = await scheduler.postTask(() => {});
assertExact<Equals<typeof nothing, void>>();

// @ts-expect-error The result is a number, not a string.
assertType<string>(await scheduler.postTask(() => 42));

// An explicit `any` type argument keeps the previous behavior.
assertType<Promise<any>>(scheduler.postTask<any>(() => 1));
}
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