K Radius Subarray Averages LeetCode solution in JavaScript

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var getAverages = function (nums, k) {
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  const twoK = 2 * k;
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  const windowSize = twoK + 1;
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  const result = [...nums].fill(-1);
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  let sum = 0;
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  for (let i = 0; i < nums.length; i++) {
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    sum += nums[i];
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    if (i >= twoK) {
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      result[i - k] = Math.floor(sum / windowSize);
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      sum -= nums[i - twoK];
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    }
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  }
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  return result;
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};