fix: don't make wheel events passive by default (#13322)

This was done previously to align with browser behavior, but the browser behavior actually only makes them passive on window/document/body. Since wheel events are not delegated, we can revert their passive-by-default setting. Closes #13318

For touchstart/touchmove we're not changing it because these events are delegated, which means they happen a lot more often on a target higher up the tree, which may cause jank.

Author: dummdidumm

.changeset/new-baboons-fetch.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: don't make wheel events passive by default

documentation/docs/02-template-syntax/02-basic-markup.md

@@ -112,7 +112,7 @@ Because events are just attributes, the same rules as for attributes apply:
 
 Timing-wise, event attributes always fire after events from bindings (e.g. `oninput` always fires after an update to `bind:value`). Under the hood, some event handlers are attached directly with `addEventListener`, while others are _delegated_.
 
-When using `onwheel`, `onmousewheel`, `ontouchstart` and `ontouchmove` event attributes, the handlers are [passive](https://developer.mozilla.org/en-US/docs/Web/API/EventTarget/addEventListener#using_passive_listeners) to align with browser defaults. This greatly improves responsiveness by allowing the browser to scroll the document immediately, rather than waiting to see if the event handler calls `event.preventDefault()`.
+When using `ontouchstart` and `ontouchmove` event attributes, the handlers are [passive](https://developer.mozilla.org/en-US/docs/Web/API/EventTarget/addEventListener#using_passive_listeners) for better performance. This greatly improves responsiveness by allowing the browser to scroll the document immediately, rather than waiting to see if the event handler calls `event.preventDefault()`.
 
 In the very rare cases that you need to prevent these event defaults, you should use [`on`](https://svelte-5-preview.vercel.app/docs/imports#svelte-events) instead (for example inside an action).
 

packages/svelte/src/utils.js

@@ -222,7 +222,16 @@ export function is_dom_property(name) {
 	return DOM_PROPERTIES.includes(name);
 }
 
-const PASSIVE_EVENTS = ['wheel', 'mousewheel', 'touchstart', 'touchmove'];
+/**
+ * Subset of delegated events which should be passive by default.
+ * These two are already passive via browser defaults on window, document and body.
+ * But since
+ * - we're delegating them
+ * - they happen often
+ * - they apply to mobile which is generally less performant
+ * we're marking them as passive by default for other elements, too.
+ */
+const PASSIVE_EVENTS = ['touchstart', 'touchmove'];
 
 /**
  * Returns `true` if `name` is a passive event