Find Players With Zero or One Losses LeetCode solution in JavaScript

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/**
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 * @param {number[][]} matches
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 * @return {number[][]}
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 */
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var findWinners = function (matches) {
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  var looser = {};
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  var allPlayer = {};
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  for (var i = 0; i < matches.length; i++) {
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    if (looser[matches[i][1]]) looser[matches[i][1]]++;
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    else looser[matches[i][1]] = 1;
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    if (!allPlayer[matches[i][0]]) allPlayer[matches[i][0]] = 1;
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    if (!allPlayer[matches[i][1]]) allPlayer[matches[i][1]] = 1;
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  }
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  var first = [],
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    second = [];
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  for (var key in allPlayer) {
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    if (!looser[key]) first.push(key);
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    if (looser[key] == 1) second.push(key);
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  }
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  return [first, second];
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};