addtolast.js

    addToLast(data) {
        let newNode = new node(data);
        /*
       If the list is empty , 
       newly created `node` 
       will be the `head` of the list.
       */
        
        if (this.head == null) {
            this.head = newNode;
        }
        /*
        if not,traverse through the list recursively 
        until `next` of the `currentnode` is null 
        and then point `next` of the `currentnode`
        to the newly created `node`.
        */
        else {
            let currentNode = this.head;
            while (currentNode.next != null) {
                currentNode = currentNode.next;
            }
            currentNode.next = newNode;
        }
        /*
        increment length
        */
        this.length++;
    }