Max Difference You Can Get From Changing an Integer LeetCode solution in JavaScript

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var maxDiff = function (num) {
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  let occur = undefined;
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  let max = num.toString().split("");
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  let min = num.toString().split("");
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  for (i = 0; i < max.length; i++) {
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    if (max[i] < 9 && !occur) {
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      occur = max[i];
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      max[i] = 9;
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    }
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    if (max[i] === occur) max[i] = 9;
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  }
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  occur = undefined;
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  let zerone;
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  for (i = 0; i < min.length; i++) {
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    if (!occur && min[i] > 1) {
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      occur = min[i];
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      if (i === 0) zerone = 1;
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      else zerone = 0;
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      min[i] = zerone;
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    }
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    if (min[i] === occur) min[i] = zerone;
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  }
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  return +max.join("") - +min.join("");
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};