Element Appearing More Than 25% In Sorted Array LeetCode solution in JavaScript

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function binarySearch(array, target, findFirst) {
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  function helper(start, end) {
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    if (start > end) {
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      return -1;
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    }
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    const middle = Math.floor((start + end) / 2);
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    const value = array[middle];
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    if (value === target) {
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      if (findFirst) {
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        if (middle === 0 || array[middle - 1] !== value) {
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          return middle;
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        }
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        return helper(start, middle - 1);
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      } else {
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        if (middle === array.length - 1 || array[middle + 1] !== value) {
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          return middle;
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        }
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        return helper(middle + 1, end);
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      }
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    } else if (value < target) {
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      return helper(middle + 1, end);
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    }
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    return helper(start, middle - 1);
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  }
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  return helper(0, array.length - 1);
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}
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const findFirstOccurance = (array, target) => binarySearch(array, target, true);
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const findLastOccurance = (array, target) => binarySearch(array, target, false);
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var findSpecialInteger = function (arr) {
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  for (const i of [
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    Math.floor(arr.length / 4),
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    Math.floor(arr.length / 2),
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    Math.floor((3 * arr.length) / 4),
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  ]) {
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    const firstOccurance = findFirstOccurance(arr, arr[i]);
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    const lastOccurance = findLastOccurance(arr, arr[i]);
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    if (lastOccurance - firstOccurance + 1 > arr.length / 4) {
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      return arr[i];
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    }
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  }
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  return -1;
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};