fix event typings (#4066)

Author: JoviDeCroock

src/jsx.d.ts

@@ -1076,9 +1076,9 @@ export namespace JSXInternal {
 	export type TargetedPictureInPictureEvent<Target extends EventTarget> =
 		TargetedEvent<Target, PictureInPictureEvent>;
 
-	export interface EventHandler<E extends TargetedEvent> {
-		(this: void, event: E): void;
-	}
+	export type EventHandler<E extends TargetedEvent> = {
+		bivarianceHack(event: E): void;
+	}['bivarianceHack'];
 
 	export type AnimationEventHandler<Target extends EventTarget> = EventHandler<
 		TargetedAnimationEvent<Target>

test/ts/Component-test.tsx

@@ -122,6 +122,19 @@ function Mapper() {
 	return [1, 2, 3].map(x => <MapperItem foo={x} key={x} />);
 }
 
+class Button extends Component {
+	handleClick(this: HTMLButtonElement, event: MouseEvent) {
+		event.preventDefault();
+		if (event.target instanceof HTMLElement) {
+			console.log(event.target.localName);
+		}
+	}
+
+	render() {
+		return <button onClick={this.handleClick}>{this.props.children}</button>;
+	}
+}
+
 describe('Component', () => {
 	const component = new SimpleComponent({ initialName: 'da name' });