Max Sum of a Pair With Equal Sum of Digits LeetCode solution in JavaScript

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var maximumSum = function (nums) {
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  let sums = nums.map((x) =>
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    x
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      .toString()
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      .split("")
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      .map(Number)
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      .reduce((a, b) => a + b, 0)
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  );
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  let max = -1;
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  let map = sums.reduce((a, b, c) => {
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    a[b] ??= [];
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    a[b].push(nums[c]);
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    return a;
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  }, {});
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  Object.values(map).forEach((x) => {
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    if (x.length > 1) {
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      let temp = x.sort((a, b) => b - a);
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      max = Math.max(max, temp[0] + temp[1]);
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    }
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  });
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  return max;
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};