seitu/dist/core/throttled/index.mjs

import { createReadableSubscription, createSubscription } from "../subscription/index.mjs";
//#region src/core/throttled/index.ts
/**
* Throttles updates from a source to at most once per `wait` ms (leading, then
* trailing). Unsubscribed `get()` reads through; subscribed `get()` returns the
* last emitted value.
*
* @example
* ```ts twoslash
* import { createStore, createThrottled } from 'seitu'
*
* const store = createStore('')
* const throttled = createThrottled(store, 300)
* throttled.subscribe(value => console.log('throttled:', value))
* ```
*/
function createThrottled(source, wait) {
	let state = source.get();
	let timeoutId;
	let hasTrailing = false;
	let active = false;
	const cancel = () => {
		clearTimeout(timeoutId);
		timeoutId = void 0;
		hasTrailing = false;
	};
	const { subscribe, notify } = createSubscription({ onFirstSubscribe() {
		state = source.get();
		active = true;
		const unsubscribe = source.subscribe(() => {
			if (timeoutId) {
				hasTrailing = true;
				return;
			}
			state = source.get();
			notify();
			timeoutId = setTimeout(() => {
				timeoutId = void 0;
				if (hasTrailing) {
					hasTrailing = false;
					state = source.get();
					notify();
				}
			}, wait);
		});
		return () => {
			cancel();
			active = false;
			unsubscribe();
		};
	} });
	const flush = () => {
		if (!hasTrailing) {
			cancel();
			return;
		}
		cancel();
		state = source.get();
		notify();
	};
	const get = () => active ? state : source.get();
	return {
		...createReadableSubscription(get, subscribe, notify, source.getServer),
		cancel,
		flush
	};
}
//#endregion
export { createThrottled };