Check if a linked list is looping

function checkForLoopage(node) {
  if (node === null) return false;

  let fast = node.next;
  let slow = node;

  while (fast !== null && fast.next !== null) {
    if (fast === slow) return true;
    else {
      fast = fast.next.next;
      slow = slow.next;
    }
  }
  return false;
}

OR

var hasCycle = function(head) {
    let fastPointer = head;
    let slowPointer = head;
    
    while (fastPointer && fastPointer.next) {
        fastPointer = fastPointer.next.next;
        slowPointer = slowPointer.next;;
        
        if (fastPointer === slowPointer) {
            return true
        }
    }

    return false;
};