async-timeout-js/asynctimeout.js

const is_promise = obj => !!obj && (typeof obj === 'object' || typeof obj === 'function') && typeof obj.then === 'function';

const fire_and_forget = (a, on_error) => {
	(async () => {
		try {
			await a();
		} catch(e) { if(on_error) on_error(e); else throw(e); }
	})();
};
/// An async wrapper around `setTimeout()` and `setInterval()`. 
///
/// # `setTimeout()`
/// `await (new AsyncTimeout(() => "value", 100)).timeout() /* === "value" */` is `setTimeout(()=> "value", 100)` promisified.
///
/// # `setInterval()`
/// `for await (const value of new AsyncTimeout(() => "value", 100)).interval()) { /* value === "value" */ }` is `setInterval(()=> "value", 100)` promisified.
/// This is an infinite iterator. To cancel the interval, simply break out of the `for await` loop.
///
/// # Parameters
/// * `thing` - The function to call after the timeout/interval. The result of the promise (or the yield for `interval()`) is the result of this function call. If the funtion throws, then the rejection of the promise will be that error thrown.
/// * `interval` - The time to wait for the timeout or interval
///
/// # Examples
/// See `examples` below.
function AsyncTimeout(thing, interval)
{
	this.timeout = () => new Promise((resolve, reject) => {
		setTimeout(() => {
			const eval_thing = () => {
				try {
					return thing();
				} catch(e) { reject(e); }
			};
			const rv = eval_thing();
			if(is_promise(rv)) fire_and_forget(async () => resolve(await rv), reject);
			else resolve(rv);
		}, interval);
	});
	this.interval = async function*() {
		while(true) {
			yield await new Promise((resolve, reject) => {
				const eval_thing = () => {
					try {
						return thing();
					} catch(e) { reject(e); }
				};
				setTimeout(() => {
					const irv = eval_thing();
					if(is_promise(irv)) fire_and_forget(async() => resolve(await irv), reject);
					else resolve(irv);
				}, interval);
			});
		}
	};
}

/// Return a promise that will resolve when the timeout `i` has completed. There is no value for this resolution.
AsyncTimeout.await_timeout = (i) => new AsyncTimeout(() => {}, i).timeout();
/// Return an async iterator that will resolve the next iteration every `i`. There is no value for these yielded resolutions.
AsyncTimeout.await_interval = (i) => new AsyncTimeout(() => {}, i).interval();

/// Cancellation token source for `timeout_example`
function Cancellation() { 
	let tokens = [];

	this.cancel_after_interrupt = (sig) => new Promise(resolve => {
		sig = sig || 'SIGINT';
		process.on(sig, () => { 
			//console.log(`>>> Received signal ${sig}`);
			resolve(sig || "<signal>");
		});
	});


	this.cancel_after_invoke = () => new Promise(resolve => {
		tokens.push(resolve);
	});

	this.cancel_invoke = (value) => tokens.shift()(value || "<invoked>");
}

/// Run the timeout example
const timeout_example = async (_timeout, cancelAfter) => {
	_timeout = _timeout || 100;
	let cancel = false;

	const canceller = new Promise(resolve => {
		if(is_promise(cancelAfter)) (async () => {
			resolve(cancel = ((await cancelAfter) || true));
		})();
		else if(cancelAfter && cancelAfter > 0) setTimeout(() => resolve(cancel = true), cancelAfter);
		else resolve(false);
	});

	// Wait _timeout then alert "hi"
	console.log(await (new AsyncTimeout(() => "hi", _timeout)).timeout());

	// Wait _timeout then call then await this async lambda, then print its result.
	console.log(await (new AsyncTimeout(async () => {
		console.log("> Hi starting promise...");
		await AsyncTimeout.await_timeout(_timeout);
		console.log(">> Hi inside promise!");
		await AsyncTimeout.await_timeout(_timeout);
		console.log("> Hi ending promise...");
		return "hi, from async lambda!";
	}, _timeout)).timeout());

	// Wait _timeout as with this async lambda which uses `.interval()` producing the result `(_timeout / 10) || 10` times.
	console.log(await (new AsyncTimeout(async () => {
		let i=0;
		const len = (_timeout / 10) || 10;
		for await (const value of AsyncTimeout.await_interval(_timeout)) {
			console.log(`[al]: iteration ${i}`);
			i+=1;
			if(cancel) throw "Operation cancelled.";
			else if(i == len) return `Hi from async lambda containing iterator!, Completed ${i} iterations`;
		}
	}, _timeout)).timeout());

	// Wait _timeout as interval running at most `(_interval / 10) || 10` times
	console.log(await (async () => {
		let i=0;
		const len = (_timeout / 10) || 10;
		for await (const value of new AsyncTimeout(async () => {
			console.log(`i > Waiting ${_timeout * 2}`);
			await AsyncTimeout.await_timeout(_timeout * 2);
			console.log(`i > Returning ${i} as iteration value.`);
			return `${i}`;
		}, _timeout).interval()) { 
			console.log(`!i >>> Iteration ${i}`);
			i += 1;
			if(cancel) throw "Operation cancelled.";
			else if(i == len) return value;
		}
	})());

	// Continuously wait _timeout then alert "hi forever", until `cancelAfter` is reached (if it is)
	for await (const value of new AsyncTimeout(() => "hi forever", _timeout).interval()) { if(cancel) break; console.log(value); }

	// Return `true` if cancelled (or, if `cancelAfter` was a promise that returned a truthy value, that resolved value); `false` if not (should never happen)
	return await canceller;
};

/// Run the timeout example, catching an error if there is one thrown (usually on cancellation.)
const try_example = async (time) => { 
	try { return { value: await timeout_example(null, time) }; }
	catch(e) { console.log(`Error! ${e}`); return {error: e}; } 
};

//try_example(2500); // Error! Operation cancelled. -> `{ error: "Operation cancelled." }`
//try_example(5000); // -> `{ value: true }`