Binary Search Tree Iterator LeetCode solution in JavaScript

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/**
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 * Definition for a binary tree node.
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 * function TreeNode(val, left, right) {
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 *     this.val = (val===undefined ? 0 : val)
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 *     this.left = (left===undefined ? null : left)
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 *     this.right = (right===undefined ? null : right)
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 * }
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 */
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/**
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 * @param {TreeNode} root
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 */
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var BSTIterator = function (root) {
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  this.stack = [];
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  this.node = root;
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};
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/**
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 * @return {number}
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 */
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BSTIterator.prototype.next = function () {
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  while (this.node) {
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    this.stack.push(this.node);
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    this.node = this.node.left;
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  }
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  const node = this.stack.pop();
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  this.node = node.right;
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  return node.val;
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};
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/**
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 * @return {boolean}
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 */
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BSTIterator.prototype.hasNext = function () {
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  return this.node || this.stack.length > 0;
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};
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/**
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 * Your BSTIterator object will be instantiated and called as such:
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 * var obj = new BSTIterator(root)
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 * var param_1 = obj.next()
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 * var param_2 = obj.hasNext()
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 */