a_list.js

function arrayToList(array) {
	let list = null;
	for (let i = 0; i < array.length; i++) {
		list = { value: array[i], rest: list };
	}
	return list;
}

function listToArray(list) {
	let array = [];
	for (let node = list; node; node = node.rest) {
		array.push(node.value);
	}
	return array;
}

function prepend(value, list) {
	return { value, rest: list };
}

function nth(list, n) {
	if (!list) return undefined;
	else if (n == 0) return list.value;
	else return nth(list.rest, n - 1);
}

console.log(arrayToList([10, 20, 30]));
console.log(listToArray(arrayToList([10, 20, 30])));
console.log(prepend(10, prepend(20, null)));
console.log(nth(arrayToList([10, 20, 30]), 1));