Get node value in a linked list position from tail | JS

getNode.js

function getNode(head, positionFromTail) {

    var length =0;
    var tp = head;
    while(tp!==null){
        length++;
        tp=tp.next
    }
   let currentPosition=0;
    if(head==null){
        return head;
    }else{
        while(currentPosition < length-positionFromTail-1 && head.next!==null){
            
            head=head.next;
            currentPosition++;
        }

        return(head.data);
    }


}

Get node value in a linked list position from tail | JS