How to determine if two singly linked lists intersect

function intersection(list1, list2) {
  let len1 = 0;
  let len2 = 0;
  
  let l1 = list1;
  let l2 = list2;
  let tail1, tail2;
  
  while (l1) {
    len1++;
    if (!l1.next) tail1 = l1;
    l1 = l1.next;  
  }
  while (l2) {
    len2++;
    if (!l2.next) tail2 = l2;
    l2 = l2.next;
  }
  
  if (tail1 !== tail2) return null; // tails should match if there is an intersection
  let lenDiff = Math.abs(len2-len1);
  if (len2 > len1) {
    while (lenDiff--) {
      list2 = list2.next;
    }
  } else {
    while (lenDiff--) {
      list1 = list1.next;
    }
  }
  
  
  while (list1 && list2) {
    
    if (list1 === list2) return list1;
    
    list1 = list1.next;
    list2 = list2.next;
  }
}
function Node(data) {
  this.next = null;
  this.data = data;
}
Node.prototype.addToTail = function(data) {
  const end = new Node(data);
  let current = this;
  while (current.next !== null) {
    current = current.next;
  }
  current.next = end;
  return end;
};