binarySearch.js

let binarySearch = (arr, left, right, searchValue) => {
  if (left <= right) {
    middle = Math.floor((left + (right - left) / 2))
    if (searchValue === arr[middle]) {
      return middle
    }

    if (searchValue < arr[middle]) {
      return binarySearch(arr, left, middle - 1, searchValue)
    } else {
      return binarySearch(arr, middle + 1, right, searchValue)
    }
  }

  return -1
}

let arr = [1, 2, 3, 4, 9]

console.log("Index of 9 element = "+binarySearch(arr, 0, arr.length - 1, 9))