class Node {
    constructor(data, next) {
        this.data = data;
        this.next = next;
    }
}

function createListFromArray(array) {
    let list = null;
    for (const item of array) {
        list = new Node(item, list);
    }
    return list;
}

function displayList(list) {
    while (list) {
        console.log(list.data);
        list = list.next;
    }
}

function length(head) {
    let length = 0;

    while (head != null) {
        length++;
        head = head.next;
    }

    return length;
}

let array = [3,2,1];
let list = createListFromArray(array);
console.log(length(list));