Find Lucky Integer in an Array LeetCode solution in JavaScript

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// time O(n) space O(n)
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var findLucky = function (arr) {
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  let max = -1;
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  const map = {};
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  for (const number of arr) {
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    if (map[number]) {
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      map[number] += 1;
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    } else {
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      map[number] = 1;
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    }
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  }
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  for (const key in map) {
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    if (Number(key) === map[key] && map[key] > max) {
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      max = map[key];
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    }
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  }
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  return max;
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};