Construct Binary Search Tree from Preorder Traversal.js

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {number[]} preorder
 * @return {TreeNode}
 */

 function TreeNode(val) {
     var node = {};
     node.val = val;
     node.left = node.right = null;
     return node;
 }

var bstFromPreorder = function(preorder) {
    var root = TreeNode(preorder[0]);
    var stack = [root];
    for (var i = 1; i < preorder.length; i++) {
        var temp = null;  
  
        // Keep on popping while the next value is greater than  
        // stack's top value.
        while ( stack.length > 0 && preorder[i] > stack[stack.length - 1].val )  
            temp = stack.pop();  
  
        // Make this greater value as the right child 
        // and push it to the stack 
        if ( temp != null)  
        {  
            temp.right = TreeNode(preorder[i]);  
            stack.push(temp.right);    
        // If the next value is less than the stack's top 
        // value, make this value as the left child of the 
        // stack's top node. Push the new node to stack 
        } else {  
            stack[stack.length - 1].left = TreeNode(preorder[i]);  
            stack.push(stack[stack.length - 1].left);  
        }  
    }
    return root;
};