Avoiding to overfill the stack thanks to setTimeout

factorialAndTimeout.js

const smallValue = 100;
const largeValue = 50000;

function factorial(n) {
	return (n !== 0) ? n * factorial(n - 1) : 1;
}

function tailFactorial(n, total = 1) {
    //console.trace();
    if (n === 0) {
        return total;
    }    // proper tail call
    return tailFactorial(n - 1, n * total);
}

function runFactorial(factorialFn){
	let res = factorialFn(smallValue);
	console.log("factorial: " + res);

	//stack overflow:
	try {
		res = factorialFn(largeValue);
		console.log("factorial: " + res);
	}
	catch (ex){
		console.log("Exception: " + ex.message);
		//Maximum call stack size exceeded
	}
}

[factorial, tailFactorial].forEach(fn => runFactorial(fn));
//for both functions we get a max stack exception, so node no longer implements TCO


//--------------------------




function factorialWithTimeoutAndPromise(n, total = 1, resFn){
	//initial call	
	if (resFn === undefined){
		var pr = new Promise((res, rej) => resFn = res);
	}
	if (n === 0){
		resFn(total);
	}
	else{
		setTimeout(() => factorialWithTimeoutAndPromise(n-1, n * total, resFn), 0);
	}
	return pr;
}

function factorialWithTimeoutAndPromiseImproved(n, total = 1, counter = 0, resFn){
	//initial call	
	if (resFn === undefined){
		var pr = new Promise((res, rej) => resFn = res);
	}
	if (n === 0){
		resFn(total);
	}
	else{
		if (counter < 50){
			factorialWithTimeoutAndPromiseImproved(n-1, n * total, ++counter, resFn);
		}
		else{
			setTimeout(() => factorialWithTimeoutAndPromiseImproved(n-1, n * total, 0, resFn), 0);
		}
	}
	return pr;
}

(async() => {
	console.log("-- using Timeout");

	let options = [
		{ 
			name: "Not optimized",
			value: smallValue,
			fn: factorialWithTimeoutAndPromise
		},
		{ 
			name: "Not optimized",
			value: largeValue,
			fn: factorialWithTimeoutAndPromise
		},
		{ 
			name: "Optimized",
			value: smallValue,
			fn: factorialWithTimeoutAndPromiseImproved
		},
		{ 
			name: "Optimized",
			value: largeValue,
			fn: factorialWithTimeoutAndPromiseImproved
		}
	];
 
	for (let option of options) {
		console.log(option.name + " factorial for: " + option.value);
		let start = Date.now();
		let result = await option.fn(option.value);
		console.log("result: " + result);
		console.log("it took " + (Date.now() - start) + "\n");
	}
})();