fix: better types for on

- give autocompletion for types and more precise event types for html elements
- allow to pass other kinds of event target nodes, like window

closes #12027
fixes #12045

Author: dummdidumm

.changeset/rare-insects-tell.md

@@ -0,0 +1,5 @@
+---
+"svelte": patch
+---
+
+fix: better types for `on`

packages/svelte/src/internal/client/dom/elements/events.js

@@ -33,7 +33,7 @@ export function replay_events(dom) {
 
 /**
  * @param {string} event_name
- * @param {Element} dom
+ * @param {EventTarget} dom
  * @param {EventListener} handler
  * @param {AddEventListenerOptions} options
  */
@@ -71,7 +71,31 @@ export function create_event(event_name, dom, handler, options) {
  * rather than `addEventListener` will preserve the correct order relative to handlers added declaratively
  * (with attributes like `onclick`), which use event delegation for performance reasons
  *
+ * @template {HTMLElement} Element
+ * @template {keyof HTMLElementEventMap} Type
+ * @overload
  * @param {Element} element
+ * @param {Type} type
+ * @param {(this: Element, event: HTMLElementEventMap[Type]) => any} handler
+ * @param {AddEventListenerOptions} [options]
+ * @returns {() => void}
+ */
+
+/**
+ * Attaches an event handler to an element and returns a function that removes the handler. Using this
+ * rather than `addEventListener` will preserve the correct order relative to handlers added declaratively
+ * (with attributes like `onclick`), which use event delegation for performance reasons
+ *
+ * @overload
+ * @param {EventTarget} element
+ * @param {string} type
+ * @param {EventListener} handler
+ * @param {AddEventListenerOptions} [options]
+ * @returns {() => void}
+ */
+
+/**
+ * @param {EventTarget} element
  * @param {string} type
  * @param {EventListener} handler
  * @param {AddEventListenerOptions} [options]
@@ -119,12 +143,12 @@ export function delegate(events) {
 }
 
 /**
- * @param {Node} handler_element
+ * @param {EventTarget} handler_element
  * @param {Event} event
  * @returns {void}
  */
 export function handle_event_propagation(handler_element, event) {
-	var owner_document = handler_element.ownerDocument;
+	var owner_document = /** @type {Node} */ (handler_element).ownerDocument;
 	var event_name = event.type;
 	var path = event.composedPath?.() || [];
 	var current_target = /** @type {null | Element} */ (path[0] || event.target);

packages/svelte/tests/types/events.ts

@@ -0,0 +1,28 @@
+import { on } from 'svelte/events';
+
+// ---------------- on
+
+on(document.body, 'click', (e) => e.button);
+
+on(
+	document.body,
+	'clidck',
+	(e) =>
+		// @ts-expect-error
+		e.button
+);
+
+on(
+	window,
+	'click',
+	(e) =>
+		// @ts-expect-error ideally we'd know this is a MouseEvent here, too, but for keeping the types sane, we currently don't
+		e.button
+);
+
+on(
+	// @ts-expect-error
+	'asd',
+	'asd',
+	(e) => e
+);

packages/svelte/types/index.d.ts

@@ -2350,9 +2350,15 @@ declare module 'svelte/events' {
 	 * rather than `addEventListener` will preserve the correct order relative to handlers added declaratively
 	 * (with attributes like `onclick`), which use event delegation for performance reasons
 	 *
-	 * 
-	 */
-	export function on(element: Element, type: string, handler: EventListener, options?: AddEventListenerOptions | undefined): () => void;
+	 * */
+	export function on<Element extends HTMLElement, Type extends keyof HTMLElementEventMap>(element: Element, type: Type, handler: (this: Element, event: HTMLElementEventMap[Type]) => any, options?: AddEventListenerOptions | undefined): () => void;
+	/**
+	 * Attaches an event handler to an element and returns a function that removes the handler. Using this
+	 * rather than `addEventListener` will preserve the correct order relative to handlers added declaratively
+	 * (with attributes like `onclick`), which use event delegation for performance reasons
+	 *
+	 * */
+	export function on(element: EventTarget, type: string, handler: EventListener, options?: AddEventListenerOptions | undefined): () => void;
 }
 
 declare module 'svelte/types/compiler/preprocess' {