Write a function arrayToList that builds up a data structure like the previous one when given [1, 2, 3] as argument, and write a listToArray function that produces an array from a list. Also write the helper functions prepend, which takes an element and a list and creates a new list that adds the element to the front of the input list, and nth, …

arraytolist_and_listtoarray.js

function arrayToList(array) {
	var list=null;
  	for (var i=array.length - 1; i >= 0; i--) {
    	list = {value:array[i], rest:list};
    }
  	return list;
}

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

function prepend(value, list) {
	return {value: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([3,5,7]));
console.log(listToArray(arrayToList([3,5,7])));
console.log(prepend(30,prepend(4,0)));
console.log(nth(arrayToList([4,6,2,21,2]),3));