Convert Sorted Array to Binary Search Tree

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {number[]} nums
 * @return {TreeNode}
 */
var sortedArrayToBST = function(nums) {
    if(!nums.length) return null;
    const result = new TreeNode(nums)
    return result
};

function TreeNode(nums) {
    if(nums.length){
        const middleIndex = Math.floor(nums.length/2)
        this.val = nums[middleIndex];
        if(middleIndex>0){
             this.left =  new TreeNode(nums.slice(0, middleIndex));
        } else {
             this.left =  null
        }
        if(middleIndex<nums.length-1){
            this.right = new TreeNode(nums.slice(middleIndex+1));
       } else {
           this.right = null
       }
    } else { return null }
}