apps.apple.com/node_modules/svelte/src/runtime/internal/scheduler.js

import { run_all } from './utils.js';
import { current_component, set_current_component } from './lifecycle.js';

export const dirty_components = [];
export const intros = { enabled: false };
export const binding_callbacks = [];

let render_callbacks = [];

const flush_callbacks = [];

const resolved_promise = /* @__PURE__ */ Promise.resolve();

let update_scheduled = false;

/** @returns {void} */
export function schedule_update() {
	if (!update_scheduled) {
		update_scheduled = true;
		resolved_promise.then(flush);
	}
}

/** @returns {Promise<void>} */
export function tick() {
	schedule_update();
	return resolved_promise;
}

/** @returns {void} */
export function add_render_callback(fn) {
	render_callbacks.push(fn);
}

/** @returns {void} */
export function add_flush_callback(fn) {
	flush_callbacks.push(fn);
}

// flush() calls callbacks in this order:
// 1. All beforeUpdate callbacks, in order: parents before children
// 2. All bind:this callbacks, in reverse order: children before parents.
// 3. All afterUpdate callbacks, in order: parents before children. EXCEPT
//    for afterUpdates called during the initial onMount, which are called in
//    reverse order: children before parents.
// Since callbacks might update component values, which could trigger another
// call to flush(), the following steps guard against this:
// 1. During beforeUpdate, any updated components will be added to the
//    dirty_components array and will cause a reentrant call to flush(). Because
//    the flush index is kept outside the function, the reentrant call will pick
//    up where the earlier call left off and go through all dirty components. The
//    current_component value is saved and restored so that the reentrant call will
//    not interfere with the "parent" flush() call.
// 2. bind:this callbacks cannot trigger new flush() calls.
// 3. During afterUpdate, any updated components will NOT have their afterUpdate
//    callback called a second time; the seen_callbacks set, outside the flush()
//    function, guarantees this behavior.
const seen_callbacks = new Set();

let flushidx = 0; // Do *not* move this inside the flush() function

/** @returns {void} */
export function flush() {
	// Do not reenter flush while dirty components are updated, as this can
	// result in an infinite loop. Instead, let the inner flush handle it.
	// Reentrancy is ok afterwards for bindings etc.
	if (flushidx !== 0) {
		return;
	}
	const saved_component = current_component;
	do {
		// first, call beforeUpdate functions
		// and update components
		try {
			while (flushidx < dirty_components.length) {
				const component = dirty_components[flushidx];
				flushidx++;
				set_current_component(component);
				update(component.$$);
			}
		} catch (e) {
			// reset dirty state to not end up in a deadlocked state and then rethrow
			dirty_components.length = 0;
			flushidx = 0;
			throw e;
		}
		set_current_component(null);
		dirty_components.length = 0;
		flushidx = 0;
		while (binding_callbacks.length) binding_callbacks.pop()();
		// then, once components are updated, call
		// afterUpdate functions. This may cause
		// subsequent updates...
		for (let i = 0; i < render_callbacks.length; i += 1) {
			const callback = render_callbacks[i];
			if (!seen_callbacks.has(callback)) {
				// ...so guard against infinite loops
				seen_callbacks.add(callback);
				callback();
			}
		}
		render_callbacks.length = 0;
	} while (dirty_components.length);
	while (flush_callbacks.length) {
		flush_callbacks.pop()();
	}
	update_scheduled = false;
	seen_callbacks.clear();
	set_current_component(saved_component);
}

/** @returns {void} */
function update($$) {
	if ($$.fragment !== null) {
		$$.update();
		run_all($$.before_update);
		const dirty = $$.dirty;
		$$.dirty = [-1];
		$$.fragment && $$.fragment.p($$.ctx, dirty);
		$$.after_update.forEach(add_render_callback);
	}
}

/**
 * Useful for example to execute remaining `afterUpdate` callbacks before executing `destroy`.
 * @param {Function[]} fns
 * @returns {void}
 */
export function flush_render_callbacks(fns) {
	const filtered = [];
	const targets = [];
	render_callbacks.forEach((c) => (fns.indexOf(c) === -1 ? filtered.push(c) : targets.push(c)));
	targets.forEach((c) => c());
	render_callbacks = filtered;
}