Next Greater Element II LeetCode solution in JavaScript

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var nextGreaterElements = function (nums) {
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  const len = nums.length;
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  const ans = new Array(len).fill(-1);
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  const stack = [];
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  for (let i = 0; i < len; i++) {
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    if (i == 0) stack.push([i, nums[i]]);
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    else {
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      while (stack.length && stack.at(-1)[1] < nums[i]) {
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        ans[stack.pop()[0]] = nums[i];
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      }
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      stack.push([i, nums[i]]);
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    }
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  }
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  for (let num of nums) {
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    while (stack.length && stack.at(-1)[1] < num) {
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      ans[stack.pop()[0]] = num;
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    }
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  }
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  return ans;
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};