Increasing Subsequences LeetCode solution in JavaScript

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var findSubsequences = function (nums) {
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  const result = [];
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  const set = new Set();
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  function bt(index = 0, ar = []) {
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    if (!set.has(ar.join("_")) && ar.length >= 2) {
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      set.add(ar.join("_"));
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      result.push(ar);
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    }
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    for (let i = index; i < nums.length; i++) {
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      if (nums[i] >= ar[ar.length - 1] || ar.length === 0) {
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        bt(i + 1, [...ar, nums[i]]);
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      }
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    }
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  }
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  bt();
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  return result;
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};