tweak types

Author: Rich-Harris

packages/svelte/elements.d.ts

@@ -31,6 +31,8 @@
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 // TypeScript Version: 2.8
 
+import type { Attachment } from 'svelte/attachments';
+
 // Note: We also allow `null` as a valid value because Svelte treats this the same as `undefined`
 
 type Booleanish = boolean | 'true' | 'false';
@@ -862,7 +864,7 @@ export interface HTMLAttributes<T extends EventTarget> extends AriaAttributes, D
 	[key: `data-${string}`]: any;
 
 	// allow any attachment
-	[key: symbol]: (node: T) => void | (() => void);
+	[key: symbol]: Attachment<T>;
 }
 
 export type HTMLAttributeAnchorTarget = '_self' | '_blank' | '_parent' | '_top' | (string & {});

packages/svelte/src/attachments/public.d.ts

@@ -5,8 +5,8 @@
  * It can be attached to an element with an `{@attach ...}` tag, or by spreading an object containing
  * a property created with [`createAttachmentKey`](https://svelte.dev/docs/svelte/svelte-attachments#createAttachmentKey).
  */
-export interface Attachment {
-	(element: Element): void | (() => void);
+export interface Attachment<T extends EventTarget = Element> {
+	(element: T): void | (() => void);
 }
 
 export * from './index.js';

packages/svelte/types/index.d.ts

@@ -632,8 +632,8 @@ declare module 'svelte/attachments' {
 	 * It can be attached to an element with an `{@attach ...}` tag, or by spreading an object containing
 	 * a property created with [`createAttachmentKey`](https://svelte.dev/docs/svelte/svelte-attachments#createAttachmentKey).
 	 */
-	export interface Attachment {
-		(element: Element): void | (() => void);
+	export interface Attachment<T extends EventTarget = Element> {
+		(element: T): void | (() => void);
 	}
 	/**
 	 * Creates an object key that will be recognised as an attachment when the object is spread onto an element,