Searching for a range of target values in an array

Searching for a range of target values in a sorted array using binary search template 3. Original algorithm from leetcode: https://leetcode.com/explore/learn/card/binary-search/135/template-iii/936/ In my opinion, this algorithm is the best for finding "peaks". I modified it to better fit the task at hand.

by Yurii Predborskyi

JavaScript

/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number[]}
 */
const searchRange = function(nums, target) {
  // find edge function for finding start and finish
  function findEdge(left, right, direction) {
    function isEdge(i) {
      const len = i + direction;
      if (len >= 0 && len < nums.length) {
        return nums[i + direction] !== target;
      }
      return true;
    }

    function finalCheck(index) {
      if (nums[index] === target && isEdge(index)) {
        return index;
      }
      if (nums[index - direction] === target && isEdge(index - direction)) {
        return index - direction;
      }
      return -1;
    }

    while (left + 1 < right) {
      const mid = Math.floor((left + right) / 2);
      if (nums[mid] === target) {
        if (isEdge(mid)) {
          return mid;
        } else if (direction > 0) {
          left = mid;
        } else {
          right = mid;
        }
      }
      if (nums[mid] > target) {
        right = mid;
      }
      if (nums[mid] < target) {
        left = mid;
      }
    }
    return finalCheck(direction > 0 ? right : left);
  }
  // end of findEdge

  let start = -1;
  let finish = -1;
  if (nums.length < 3) {
    // nums smaller than required minimum length to find range
    // use brute force
    for (let i = 0; i < nums.length; i++) {
      if (nums[i] === target) {
        if (start === -1) {
          start = i;
        }
        finish = i;
      }
    }
  } else {
    // main function
    let left = 0;
    let right = nums.length - 1;
    let mid = 0;
    // find mid using binary search
    while (left + 1 < right) {
      mid = Math.floor((left + right) / 2);
      if (nums[mid] === target) {
        break;
      }
      if (nums[mid] > target) {
        right = mid;
      }
      if (nums[mid] < target) {
        left = mid;
      }
    }
    start = findEdge(left, mid, -1);
    finish = findEdge(mid, right, 1);
  }
  return [start, finish];
};

let tests = [{
   ...