0. function binarySearch(list, item) {
 1.   let low = 0;
 2.   let high = list.length - 1;
 3. 
 4.   while (low <= high) {
 5.     const mid = Math.round((low + high) / 2);
 6.     const guess = list[mid];
 7. 
 8.     if (guess === item) {
 9.       return mid;
10.     }
11.     if (guess > item) {
12.       high = mid - 1;
13.     } else {
14.       low = mid + 1;
15.     }
16.   }
17. 
18.   return null;
19. }