binary_search.js

const binarySearch = (arr, key) => {
  const midIdx = Math.floor(arr.length / 2)
  const midElement = arr[midIdx]

  if (midElement === key) return true
  if (arr.length === 1) return false
  
  if (midElement > key) {
    return binarySearch(arr.splice(0, midIdx), key)
  }

  if (midElement < key) {
    return binarySearch(arr.splice(midIdx, arr.length), key)
  }

  return false
}

const arr = [1, 3, 5, 6, 8, 12, 23, 55, 90, 98]

console.log(binarySearch([...arr], 91)) // false
console.log(binarySearch([...arr], 23)) // true