Solution.js

var getIntersectionNode2 = function (headA, headB) {
  if (!headA || !headB) {
    return null;
  }
  let q = headA,
    p = headB;
  let lengthA = 1;
  let lengthB = 1;
  while (q.next) {
    q = q.next;
    lengthA++;
  }
  while (p.next) {
    p = p.next;
    lengthB++;
  }
  if (q !== p) {
    return null;
  }

  (q = headA), (p = headB);
  if (lengthA > lengthB) {
    for (let i = 0; i < lengthA - lengthB; i++) {
      q = q.next;
    }
  } else {
    for (let i = 0; i < lengthB - lengthA; i++) {
      p = p.next;
    }
  }
  while (q !== p && q !== null) {
    q = q.next;
    p = p.next;
  }
  return q;
};

var getIntersectionNode = function (headA, headB) {
  let p1 = headA;
  let p2 = headB;
  while (p1 != p2) {
    p1 = p1 ? p1.next : headB;
    p2 = p2 ? p2.next : headA;
  }
  return p1;
};