various

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

@@ -88,6 +88,8 @@ const all_registerd_events = new Set();
 /** @type {Set<(events: Array<string>) => void>} */
 const root_event_handles = new Set();
 
+export let run_transitions = true;
+
 /**
  * @param {string} html
  * @param {boolean} return_fragment
@@ -2547,6 +2549,8 @@ function _mount(Component, options) {
 	const container = options.target;
 	const block = create_root_block(options.intro || false);
 
+	run_transitions = options.intro ?? false;
+
 	/** @type {Exports} */
 	// @ts-expect-error will be defined because the render effect runs synchronously
 	let component = undefined;
@@ -2579,6 +2583,8 @@ function _mount(Component, options) {
 	const bound_event_listener = handle_event_propagation.bind(null, container);
 	const bound_document_event_listener = handle_event_propagation.bind(null, document);
 
+	run_transitions = true;
+
 	/** @param {Array<string>} events */
 	const event_handle = (events) => {
 		for (let i = 0; i < events.length; i++) {

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

@@ -18,6 +18,7 @@ import {
 	managed_pre_effect,
 	user_effect
 } from './reactivity/computations.js';
+import { run_transitions } from './render.js';
 import {
 	current_block,
 	current_effect,
@@ -530,7 +531,8 @@ export function bind_transition(element, get_fn, get_params, direction, global)
 
 			current_options ??= get_fn()(element, get_params?.(), { direction });
 
-			if (!current_options) {
+			if (!current_options?.duration) {
+				current_options = null;
 				callback?.();
 				return;
 			}
@@ -563,6 +565,7 @@ export function bind_transition(element, get_fn, get_params, direction, global)
 					.catch(noop);
 			} else {
 				// TODO timer
+				current_options = null;
 			}
 		}
 	};
@@ -571,9 +574,11 @@ export function bind_transition(element, get_fn, get_params, direction, global)
 	if (direction === 'in' || direction === 'both') {
 		(effect.in ??= []).push(transition);
 
-		user_effect(() => {
+		if (run_transitions) {
-			transition.to(1);
+			user_effect(() => {
-		});
+				untrack(() => transition.to(1));
+			});
+		}
 	}
 
 	if (direction === 'out' || direction === 'both') {