Find the Difference LeetCode solution in JavaScript

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var findTheDifference = function (s, t) {
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  var map = {};
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  var re = "";
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  for (let i = 0; i < t.length; i++) {
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    if (t[i] in map) {
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      map[t[i]] += 1;
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    } else {
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      map[t[i]] = 1;
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    }
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  }
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  for (let i = 0; i < s.length; i++) {
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    if (s[i] in map) {
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      map[s[i]] -= 1;
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    }
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  }
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  for (let [key, value] of Object.entries(map)) {
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    if (value > 0) {
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      let temp = re.concat(key);
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      re = temp;
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    }
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  }
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  return re;
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};