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Fix Element.matches strict narrowing #2487

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Fix Element.matches strict narrowing #2487

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62a9488
Fix Element.matches strict narrowing
cjc0013 May 28, 2026
f49b6ab
Refine Element.matches narrowing map
cjc0013 Jun 30, 2026
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37 changes: 34 additions & 3 deletions baselines/dom.generated.d.ts
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Expand Up @@ -14051,9 +14051,12 @@ interface Element extends Node, ARIAMixin, Animatable, ChildNode, NonDocumentTyp
*
* [MDN Reference](https://developer.mozilla.org/docs/Web/API/Element/matches)
*/
matches<K extends keyof HTMLElementTagNameMap>(selectors: K): this is HTMLElementTagNameMap[K];
matches<K extends keyof SVGElementTagNameMap>(selectors: K): this is SVGElementTagNameMap[K];
matches<K extends keyof MathMLElementTagNameMap>(selectors: K): this is MathMLElementTagNameMap[K];
matches<K extends keyof HTMLElementTagNameMap & keyof ElementMatchesNarrowingMap<HTMLElementTagNameMap, this>>(selectors: K): this is Extract<HTMLElementTagNameMap[K], this>;
matches<K extends keyof SVGElementTagNameMap & keyof ElementMatchesNarrowingMap<SVGElementTagNameMap, this>>(selectors: K): this is Extract<SVGElementTagNameMap[K], this>;
matches<K extends keyof MathMLElementTagNameMap & keyof ElementMatchesNarrowingMap<MathMLElementTagNameMap, this>>(selectors: K): this is Extract<MathMLElementTagNameMap[K], this>;
matches<K extends keyof HTMLElementTagNameMap>(selectors: K): boolean;
matches<K extends keyof SVGElementTagNameMap>(selectors: K): boolean;
matches<K extends keyof MathMLElementTagNameMap>(selectors: K): boolean;
matches(selectors: string): boolean;
/**
* The **`releasePointerCapture()`** method of the Element interface releases (stops) pointer capture that was previously set for a specific (PointerEvent) pointer.
Expand Down Expand Up @@ -43880,6 +43883,34 @@ interface MathMLElementTagNameMap {
"semantics": MathMLElement;
}

type ElementMatchesNarrowingMap<ElementMap, ElementType> =
ElementType extends Element
? Element extends ElementType
? ElementMap
: [ElementMatchesBase<ElementType>] extends [never]
? {}
: ElementMatchesStrictMap<ElementMap, ElementMatchesBase<ElementType>>
: {};

type ElementMatchesBase<ElementType> =
HTMLElement extends ElementType
? HTMLElement
: SVGElement extends ElementType
? SVGElement
: MathMLElement extends ElementType
? MathMLElement
: never;

type ElementMatchesStrictMap<ElementMap, BaseElement> = {
[Key in keyof ElementMap as (
ElementMap[Key] extends BaseElement
? BaseElement extends ElementMap[Key]
? never
: Key
: never
)]: ElementMap[Key];
};

/** @deprecated Directly use HTMLElementTagNameMap or SVGElementTagNameMap as appropriate, instead. */
type ElementTagNameMap = HTMLElementTagNameMap & Pick<SVGElementTagNameMap, Exclude<keyof SVGElementTagNameMap, keyof HTMLElementTagNameMap>>;

Expand Down
37 changes: 34 additions & 3 deletions baselines/ts5.5/dom.generated.d.ts
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Expand Up @@ -14038,9 +14038,12 @@ interface Element extends Node, ARIAMixin, Animatable, ChildNode, NonDocumentTyp
*
* [MDN Reference](https://developer.mozilla.org/docs/Web/API/Element/matches)
*/
matches<K extends keyof HTMLElementTagNameMap>(selectors: K): this is HTMLElementTagNameMap[K];
matches<K extends keyof SVGElementTagNameMap>(selectors: K): this is SVGElementTagNameMap[K];
matches<K extends keyof MathMLElementTagNameMap>(selectors: K): this is MathMLElementTagNameMap[K];
matches<K extends keyof HTMLElementTagNameMap & keyof ElementMatchesNarrowingMap<HTMLElementTagNameMap, this>>(selectors: K): this is Extract<HTMLElementTagNameMap[K], this>;
matches<K extends keyof SVGElementTagNameMap & keyof ElementMatchesNarrowingMap<SVGElementTagNameMap, this>>(selectors: K): this is Extract<SVGElementTagNameMap[K], this>;
matches<K extends keyof MathMLElementTagNameMap & keyof ElementMatchesNarrowingMap<MathMLElementTagNameMap, this>>(selectors: K): this is Extract<MathMLElementTagNameMap[K], this>;
matches<K extends keyof HTMLElementTagNameMap>(selectors: K): boolean;
matches<K extends keyof SVGElementTagNameMap>(selectors: K): boolean;
matches<K extends keyof MathMLElementTagNameMap>(selectors: K): boolean;
matches(selectors: string): boolean;
/**
* The **`releasePointerCapture()`** method of the Element interface releases (stops) pointer capture that was previously set for a specific (PointerEvent) pointer.
Expand Down Expand Up @@ -43854,6 +43857,34 @@ interface MathMLElementTagNameMap {
"semantics": MathMLElement;
}

type ElementMatchesNarrowingMap<ElementMap, ElementType> =
ElementType extends Element
? Element extends ElementType
? ElementMap
: [ElementMatchesBase<ElementType>] extends [never]
? {}
: ElementMatchesStrictMap<ElementMap, ElementMatchesBase<ElementType>>
: {};

type ElementMatchesBase<ElementType> =
HTMLElement extends ElementType
? HTMLElement
: SVGElement extends ElementType
? SVGElement
: MathMLElement extends ElementType
? MathMLElement
: never;

type ElementMatchesStrictMap<ElementMap, BaseElement> = {
[Key in keyof ElementMap as (
ElementMap[Key] extends BaseElement
? BaseElement extends ElementMap[Key]
? never
: Key
: never
)]: ElementMap[Key];
};

/** @deprecated Directly use HTMLElementTagNameMap or SVGElementTagNameMap as appropriate, instead. */
type ElementTagNameMap = HTMLElementTagNameMap & Pick<SVGElementTagNameMap, Exclude<keyof SVGElementTagNameMap, keyof HTMLElementTagNameMap>>;

Expand Down
37 changes: 34 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 @@ -14048,9 +14048,12 @@ interface Element extends Node, ARIAMixin, Animatable, ChildNode, NonDocumentTyp
*
* [MDN Reference](https://developer.mozilla.org/docs/Web/API/Element/matches)
*/
matches<K extends keyof HTMLElementTagNameMap>(selectors: K): this is HTMLElementTagNameMap[K];
matches<K extends keyof SVGElementTagNameMap>(selectors: K): this is SVGElementTagNameMap[K];
matches<K extends keyof MathMLElementTagNameMap>(selectors: K): this is MathMLElementTagNameMap[K];
matches<K extends keyof HTMLElementTagNameMap & keyof ElementMatchesNarrowingMap<HTMLElementTagNameMap, this>>(selectors: K): this is Extract<HTMLElementTagNameMap[K], this>;
matches<K extends keyof SVGElementTagNameMap & keyof ElementMatchesNarrowingMap<SVGElementTagNameMap, this>>(selectors: K): this is Extract<SVGElementTagNameMap[K], this>;
matches<K extends keyof MathMLElementTagNameMap & keyof ElementMatchesNarrowingMap<MathMLElementTagNameMap, this>>(selectors: K): this is Extract<MathMLElementTagNameMap[K], this>;
matches<K extends keyof HTMLElementTagNameMap>(selectors: K): boolean;
matches<K extends keyof SVGElementTagNameMap>(selectors: K): boolean;
matches<K extends keyof MathMLElementTagNameMap>(selectors: K): boolean;
matches(selectors: string): boolean;
/**
* The **`releasePointerCapture()`** method of the Element interface releases (stops) pointer capture that was previously set for a specific (PointerEvent) pointer.
Expand Down Expand Up @@ -43877,6 +43880,34 @@ interface MathMLElementTagNameMap {
"semantics": MathMLElement;
}

type ElementMatchesNarrowingMap<ElementMap, ElementType> =
ElementType extends Element
? Element extends ElementType
? ElementMap
: [ElementMatchesBase<ElementType>] extends [never]
? {}
: ElementMatchesStrictMap<ElementMap, ElementMatchesBase<ElementType>>
: {};

type ElementMatchesBase<ElementType> =
HTMLElement extends ElementType
? HTMLElement
: SVGElement extends ElementType
? SVGElement
: MathMLElement extends ElementType
? MathMLElement
: never;

type ElementMatchesStrictMap<ElementMap, BaseElement> = {
[Key in keyof ElementMap as (
ElementMap[Key] extends BaseElement
? BaseElement extends ElementMap[Key]
? never
: Key
: never
)]: ElementMap[Key];
};

/** @deprecated Directly use HTMLElementTagNameMap or SVGElementTagNameMap as appropriate, instead. */
type ElementTagNameMap = HTMLElementTagNameMap & Pick<SVGElementTagNameMap, Exclude<keyof SVGElementTagNameMap, keyof HTMLElementTagNameMap>>;

Expand Down
37 changes: 34 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 @@ -14048,9 +14048,12 @@ interface Element extends Node, ARIAMixin, Animatable, ChildNode, NonDocumentTyp
*
* [MDN Reference](https://developer.mozilla.org/docs/Web/API/Element/matches)
*/
matches<K extends keyof HTMLElementTagNameMap>(selectors: K): this is HTMLElementTagNameMap[K];
matches<K extends keyof SVGElementTagNameMap>(selectors: K): this is SVGElementTagNameMap[K];
matches<K extends keyof MathMLElementTagNameMap>(selectors: K): this is MathMLElementTagNameMap[K];
matches<K extends keyof HTMLElementTagNameMap & keyof ElementMatchesNarrowingMap<HTMLElementTagNameMap, this>>(selectors: K): this is Extract<HTMLElementTagNameMap[K], this>;
matches<K extends keyof SVGElementTagNameMap & keyof ElementMatchesNarrowingMap<SVGElementTagNameMap, this>>(selectors: K): this is Extract<SVGElementTagNameMap[K], this>;
matches<K extends keyof MathMLElementTagNameMap & keyof ElementMatchesNarrowingMap<MathMLElementTagNameMap, this>>(selectors: K): this is Extract<MathMLElementTagNameMap[K], this>;
matches<K extends keyof HTMLElementTagNameMap>(selectors: K): boolean;
matches<K extends keyof SVGElementTagNameMap>(selectors: K): boolean;
matches<K extends keyof MathMLElementTagNameMap>(selectors: K): boolean;
matches(selectors: string): boolean;
/**
* The **`releasePointerCapture()`** method of the Element interface releases (stops) pointer capture that was previously set for a specific (PointerEvent) pointer.
Expand Down Expand Up @@ -43877,6 +43880,34 @@ interface MathMLElementTagNameMap {
"semantics": MathMLElement;
}

type ElementMatchesNarrowingMap<ElementMap, ElementType> =
ElementType extends Element
? Element extends ElementType
? ElementMap
: [ElementMatchesBase<ElementType>] extends [never]
? {}
: ElementMatchesStrictMap<ElementMap, ElementMatchesBase<ElementType>>
: {};

type ElementMatchesBase<ElementType> =
HTMLElement extends ElementType
? HTMLElement
: SVGElement extends ElementType
? SVGElement
: MathMLElement extends ElementType
? MathMLElement
: never;

type ElementMatchesStrictMap<ElementMap, BaseElement> = {
[Key in keyof ElementMap as (
ElementMap[Key] extends BaseElement
? BaseElement extends ElementMap[Key]
? never
: Key
: never
)]: ElementMap[Key];
};

/** @deprecated Directly use HTMLElementTagNameMap or SVGElementTagNameMap as appropriate, instead. */
type ElementTagNameMap = HTMLElementTagNameMap & Pick<SVGElementTagNameMap, Exclude<keyof SVGElementTagNameMap, keyof HTMLElementTagNameMap>>;

Expand Down
69 changes: 68 additions & 1 deletion src/build/emitter.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -645,7 +645,12 @@ export function emitWebIdl(
const paramName = m.signature[0].param![0].name;
for (const mapName of tagNameMapNames) {
printer.printLine(
`matches<K extends keyof ${mapName}>(${paramName}: K): this is ${mapName}[K];`,
`matches<K extends keyof ${mapName} & keyof ElementMatchesNarrowingMap<${mapName}, this>>(${paramName}: K): this is Extract<${mapName}[K], this>;`,
);
}
for (const mapName of tagNameMapNames) {
printer.printLine(
`matches<K extends keyof ${mapName}>(${paramName}: K): boolean;`,
);
}
printer.printLine(`matches(${paramName}: string): boolean;`);
Expand Down Expand Up @@ -715,6 +720,67 @@ export function emitWebIdl(
printer.printLine("");
}

function emitElementMatchesMap() {
printer.printLine(
"type ElementMatchesNarrowingMap<ElementMap, ElementType> =",
);
printer.increaseIndent();
printer.printLine("ElementType extends Element");
printer.increaseIndent();
printer.printLine("? Element extends ElementType");
printer.increaseIndent();
printer.printLine("? ElementMap");
printer.printLine(": [ElementMatchesBase<ElementType>] extends [never]");
printer.increaseIndent();
printer.printLine("? {}");
printer.printLine(
": ElementMatchesStrictMap<ElementMap, ElementMatchesBase<ElementType>>",
);
printer.decreaseIndent();
printer.decreaseIndent();
printer.printLine(": {};");
printer.decreaseIndent();
printer.decreaseIndent();
printer.printLine("");
printer.printLine("type ElementMatchesBase<ElementType> =");
printer.increaseIndent();
printer.printLine("HTMLElement extends ElementType");
printer.increaseIndent();
printer.printLine("? HTMLElement");
printer.printLine(": SVGElement extends ElementType");
printer.increaseIndent();
printer.printLine("? SVGElement");
printer.printLine(": MathMLElement extends ElementType");
printer.increaseIndent();
printer.printLine("? MathMLElement");
printer.printLine(": never;");
printer.decreaseIndent();
printer.decreaseIndent();
printer.decreaseIndent();
printer.decreaseIndent();
printer.printLine("");
printer.printLine(
"type ElementMatchesStrictMap<ElementMap, BaseElement> = {",
);
printer.increaseIndent();
printer.printLine("[Key in keyof ElementMap as (");
printer.increaseIndent();
printer.printLine("ElementMap[Key] extends BaseElement");
printer.increaseIndent();
printer.printLine("? BaseElement extends ElementMap[Key]");
printer.increaseIndent();
printer.printLine("? never");
printer.printLine(": Key");
printer.decreaseIndent();
printer.printLine(": never");
printer.decreaseIndent();
printer.decreaseIndent();
printer.printLine(")]: ElementMap[Key];");
printer.decreaseIndent();
printer.printLine("};");
printer.printLine("");
}

/// Emit overloads for the createEvent method
function emitCreateEventOverloads(m: Browser.Method) {
if (matchParamMethodSignature(m, "createEvent", "Event", "string")) {
Expand Down Expand Up @@ -1664,6 +1730,7 @@ export function emitWebIdl(
"MathMLElementTagNameMap",
tagNameToEleName.mathMLResult,
);
emitElementMatchesMap();
emitDeprecatedHTMLOrSVGElementTagNameMap();
emitNamedConstructors();
}
Expand Down
33 changes: 33 additions & 0 deletions unittests/files/matches.ts
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Original file line number Diff line number Diff line change
@@ -0,0 +1,33 @@
declare const element: Element;
declare const htmlElement: HTMLElement;
declare const htmlDivElement: HTMLDivElement;
declare const htmlTableCellElement: HTMLTableCellElement;

if (element.matches("dt")) {
const narrowed: HTMLElement = element;
}

if (!htmlElement.matches("dt")) {
htmlElement.id;
}

if (htmlElement.matches("td")) {
const narrowed: HTMLTableCellElement = htmlElement;
}

if (htmlElement.matches("div")) {
const narrowed: HTMLDivElement = htmlElement;
}

if (!htmlDivElement.matches("div")) {
htmlDivElement.id;
}

if (htmlDivElement.matches("object")) {
// @ts-expect-error HTMLDivElement should not narrow to HTMLObjectElement.
const narrowed: HTMLObjectElement = htmlDivElement;
}

if (!htmlTableCellElement.matches("th")) {
htmlTableCellElement.id;
}
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