Decode the Message LeetCode solution in JavaScript

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var decodeMessage = function (key, message) {
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  let result = "";
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  key = Array.from(new Set(key.split(" ").join("")));
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  const hash = new Map();
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  const alpha = "abcdefghijklmnopqrstuvwxyz";
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  for (let i = 0; i < alpha.length; i++) {
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    hash.set(key[i], alpha[i]);
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  }
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  for (let chr of message) {
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    result += hash.get(chr) || " ";
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  }
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  return result;
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};