fix

Author: Rich-Harris

packages/svelte/src/internal/client/proxy.js

@@ -9,7 +9,7 @@ import {
 	object_prototype
 } from '../shared/utils.js';
 import { check_ownership, widen_ownership } from './dev/ownership.js';
-import { source, set, state, set_call_onchange } from './reactivity/sources.js';
+import { source, set, state, batch_onchange } from './reactivity/sources.js';
 import { STATE_SYMBOL, STATE_SYMBOL_METADATA } from './constants.js';
 import { UNINITIALIZED } from '../../constants.js';
 import * as e from './errors.js';
@@ -173,16 +173,7 @@ export function proxy(value, options, parent = null, prev) {
 			const value = Reflect.get(target, prop, receiver);
 
 			if (is_proxied_array && array_methods.includes(/** @type {string} */ (prop))) {
-				// @ts-expect-error
-				return (...args) => {
-					set_call_onchange(false);
-					const result = value.apply(receiver, args);
-					set_call_onchange(true);
-
-					options?.onchange?.();
-
-					return result;
-				};
+				return batch_onchange(value);
 			}
 
 			return value;

packages/svelte/src/internal/client/reactivity/sources.js

@@ -45,11 +45,30 @@ export function set_inspect_effects(v) {
 	inspect_effects = v;
 }
 
-let call_onchange = true;
+/** @type {null | Set<() => void>} */
+let onchange_batch = null;
 
-/** @param {boolean} v */
-export function set_call_onchange(v) {
-	call_onchange = v;
+/**
+ * @param {Function} fn
+ */
+export function batch_onchange(fn) {
+	// @ts-expect-error
+	return function (...args) {
+		let previous_onchange_batch = onchange_batch;
+
+		try {
+			onchange_batch = new Set();
+
+			// @ts-expect-error
+			return fn.apply(this, args);
+		} finally {
+			for (const onchange of /** @type {Set<() => void>} */ (onchange_batch)) {
+				onchange();
+			}
+
+			onchange_batch = previous_onchange_batch;
+		}
+	};
 }
 
 /**
@@ -199,8 +218,13 @@ export function internal_set(source, value) {
 		source.v = value;
 		source.wv = increment_write_version();
 
-		if (call_onchange) {
-			untrack(() => source.o?.onchange?.());
+		var onchange = source.o?.onchange;
+		if (onchange) {
+			if (onchange_batch) {
+				onchange_batch.add(onchange);
+			} else {
+				onchange();
+			}
 		}
 
 		if (DEV && tracing_mode_flag) {