1const arr = [1, 3, 5, 7, 8, 9];
2const binarySearch = (arr, x , start=0, end=arr.length) => {
3  // If the item does not exist, return -1
4  if(end < start) return -1;
5  
6  // Calculate middle index of the array
7  let mid = Math.floor((start + end) / 2);
8  
9  // Is the middle a match?
10  if(arr[mid] === x) return mid;
11  // Is the middle less than x
12  if(arr[mid] < x) return binarySearch(arr, x, mid+1, end);
13  // Else the middle is more than x
14  else return binarySearch(arr, x , start, mid-1);
15}
16
17binarySearch(arr, 7); // Returns 3
18/* O(n) of binarySearch is log(n) */

1function binarySearch(arr, val) {
2  let start = 0;
3  let end = arr.length - 1;
4
5  while (start <= end) {
6    let mid = Math.floor((start + end) / 2);
7
8    if (arr[mid] === val) {
9      return mid;
10    }
11
12    if (val < arr[mid]) {
13      end = mid - 1;
14    } else {
15      start = mid + 1;
16    }
17  }
18  return -1;
19}
20

1function binarySearchIndex (array, target, low = 0, high = array.length - 1) {
2  if (low > high) {
3    return -1
4  }
5  const midPoint = Math.floor((low + high) / 2)
6
7  if (target < array[midPoint]) {
8    return binarySearchIndex(array, target, low, midPoint - 1)
9  } else if (target > array[midPoint]) {
10    return binarySearchIndex(array, target, midPoint + 1, high)
11  } else {
12    return midPoint
13  }
14}

1const binary = n.toString(2);