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

import { raf } from './environment.js';

const tasks = new Set();

/**
 * @param {number} now
 * @returns {void}
 */
function run_tasks(now) {
	tasks.forEach((task) => {
		if (!task.c(now)) {
			tasks.delete(task);
			task.f();
		}
	});
	if (tasks.size !== 0) raf(run_tasks);
}

/**
 * For testing purposes only!
 * @returns {void}
 */
export function clear_loops() {
	tasks.clear();
}

/**
 * Creates a new task that runs on each raf frame
 * until it returns a falsy value or is aborted
 * @param {import('./private.js').TaskCallback} callback
 * @returns {import('./private.js').Task}
 */
export function loop(callback) {
	/** @type {import('./private.js').TaskEntry} */
	let task;
	if (tasks.size === 0) raf(run_tasks);
	return {
		promise: new Promise((fulfill) => {
			tasks.add((task = { c: callback, f: fulfill }));
		}),
		abort() {
			tasks.delete(task);
		}
	};
}