Convert sorted array to binary search tree

Given an integer array nums where the elements are sorted in ascending order, convert it to a height-balanced binary search tree.

/**
 * 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
 * @return {boolean}
 */
var isValidBST = function(root) {
    function validate(node, min, max) {
        if (!node) return true;

        if ((min !== null && node.val <= min) || (max !== null && node.val >= max)) {
            return false;
        }

        return validate(node.left, min, node.val) && validate(node.right, node.val, max);
    }

    return validate(root, null, null);
};