경로 합계 - 이진 트리

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @param {number} targetSum
 * @return {boolean}
 */
var hasPathSum = function(root, targetSum) {
    if (root === null) {
    return false;
  }
  const currentSum = 0;
  return checkSum(root, targetSum, currentSum);
};

const checkSum = (root, targetSum, currentSum) => {
  if (root === null) {
    return false;
  }
  currentSum = currentSum + root.val;
  if (root.left === null && root.right === null) {
    return currentSum === targetSum;
  }

  if (root.left) {
    let bool = checkSum(root.left, targetSum, currentSum);
    if (bool) {
      return bool;
    }
  }
  if (root.right) {
    let bool = checkSum(root.right, targetSum, currentSum);
    if (bool) {
      return bool;
    }
  }
    return false;
};