Count Number of Bad Pairs LeetCode solution in JavaScript

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/**
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 * @param {number[]} nums
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 * @return {number}
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 */
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var countBadPairs = function (nums) {
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  let map = {},
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    goodPair = 0;
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  for (let i = 0; i < nums.length; i++) {
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    let value = nums[i] - i;
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    if (map[value] !== undefined) {
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      goodPair += map[value];
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      map[value]++;
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    } else {
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      map[value] = 1;
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    }
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  }
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  let n = nums.length;
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  let totalPairs = (n * (n - 1)) / 2;
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  return totalPairs - goodPair;
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};