Add Minimum Number of Rungs LeetCode solution in JavaScript

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var addRungs = function (rungs, dist) {
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  let res = 0;
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  let prev = 0;
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  for (let i = 0; i < rungs.length; i++) {
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    res += Math.floor((rungs[i] - prev - 1) / dist);
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    prev = rungs[i];
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  }
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  return res;
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};