Alphabet Board Path LeetCode solution in JavaScript

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var alphabetBoardPath = function (target) {
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  var result = "";
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  var list = "abcdefghijklmnopqrstuvwxyz";
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  var curr = 0;
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  for (i = 0; i < target.length; i++) {
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    let next = list.indexOf(target[i]);
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    if (next !== curr) {
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      if (curr === 25) (curr -= 5), (result += "U");
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      if (next % 5 !== curr % 5) {
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        diff = (next % 5) - (curr % 5);
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        if (diff > 0) (curr += diff), (result += "R".repeat(diff));
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        else (curr += diff), (result += "L".repeat(-diff));
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      }
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      diff = (next - curr) / 5;
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      if (diff > 0) (curr += diff * 5), (result += "D".repeat(diff));
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      else (curr += diff * 5), (result += "U".repeat(-diff));
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    }
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    result += "!";
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  }
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  return result;
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};