Find closest value in BST

findClosestValueInBST.js

/*
  Write a function that takes in a Binary Search Tree (BST) and a target integer
  value and returns the closest value to that target value contained in the BST.
  Each BST node has an integer value , a
  left child node, and a right child node. A node is
  said to be a valid BST node if and only if it satisfies the BST
  property: its value is strictly greater than the values of every
  node to its left; its value is less than or equal to the values
  of every node to its right; and its children nodes are either valid
  BST nodes themselves or None/null.
*/
function findClosestValueInBst(tree, target) {
  return findClosestValueInBstHelper(tree, target, Infinity)
}

const findClosestValueInBstHelper = (tree, target, closest) => {
  if (tree.value && tree.value === null) {
    return closest
  }
  if (Math.abs(tree.value - target) < Math.abs(closest - target)) {
    closest = tree.value
  }
  if (tree.value > target) {
    return findClosestValueInBstHelper(tree.left, target, closest)
  }
  else if (tree.value < target) {
    return findClosestValueInBstHelper(tree.right, target, closest)
  }
  else {
    return closest
  }
}