Find Peak Element 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 findPeakElement = function (nums) {
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  if (nums.length === 1) return 0;
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  const recursion = (startIndex, endIndex) => {
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    const midIndex = Math.floor((startIndex + endIndex) / 2);
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    if (startIndex === endIndex) return startIndex;
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    if (startIndex + 1 === endIndex) {
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      return nums[endIndex] >= nums[startIndex] ? endIndex : startIndex;
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    }
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    if (
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      nums[midIndex] > nums[midIndex - 1] &&
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      nums[midIndex] > nums[midIndex + 1]
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    )
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      return midIndex;
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    if (
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      nums[midIndex] > nums[midIndex - 1] &&
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      nums[midIndex] < nums[midIndex + 1]
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    )
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      return recursion(midIndex + 1, endIndex);
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    if (
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      nums[midIndex] < nums[midIndex - 1] &&
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      nums[midIndex] > nums[midIndex + 1]
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    )
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      return recursion(startIndex, midIndex - 1);
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    if (
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      nums[midIndex] < nums[midIndex - 1] &&
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      nums[midIndex] < nums[midIndex + 1]
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    )
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      return nums[midIndex - 1] > nums[midIndex + 1]
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        ? recursion(startIndex, midIndex - 1)
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        : recursion(midIndex + 1, endIndex);
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  };
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  return recursion(0, nums.length - 1);
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};