Data Stream as Disjoint Intervals LeetCode solution in JavaScript

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var SummaryRanges = function () {
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  this.tree = null; // { val, left?, right? }
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};
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/**
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 * @param {number} val
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 * @return {void}
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 */
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SummaryRanges.prototype.addNum = function (val) {
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  if (!this.tree) {
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    this.tree = { val };
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  } else {
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    let node = this.tree;
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    let parent, side;
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    while (node) {
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      if (node.val === val) {
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        return;
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      }
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      parent = node;
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      side = node.val > val ? "left" : "right";
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      node = node[side];
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    }
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    parent[side] = { val };
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  }
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};
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/**
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 * @return {number[][]}
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 */
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SummaryRanges.prototype.getIntervals = function () {
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  // travel from left to right
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  // generate intervals
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  // > (x === last[1] + 1) ? update last[1] : create a new one
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  const travel = (node, check) => {
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    if (!node) {
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      return;
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    }
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    travel(node.left, check);
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    check(node.val);
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    travel(node.right, check);
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  };
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  const result = [];
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  const check = (val) => {
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    if (!result.length || val > result[result.length - 1][1] + 1) {
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      result.push([val, val]);
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    } else {
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      result[result.length - 1][1] = val;
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    }
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  };
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  travel(this.tree, check);
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  return result;
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};
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/**
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 * Your SummaryRanges object will be instantiated and called as such:
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 * var obj = new SummaryRanges()
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 * obj.addNum(val)
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 * var param_2 = obj.getIntervals()
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 */