1. const binarySearch = (arr, x) => {
2.  
3.   // Initialise left and right bounds of search to start and end of arr
4.   let left_index = 0;
5.   let right_index = arr.length - 1;
6.  
7.   // While left_index and right_index have yet to overlap
8.   while (left_index <= right_index) {
9.    
10.   // Find the midpoint between left_index and right_index
11.     let mid_index = Math.floor((left_index + right_index) / 2);
12.  
13.     console.log("middle index", mid_index);
14.    
15.    // If the element at mid_index is x, return mid_index
16.     // Use Math.floor to ensure that the index position is an integer not a decimal
17.     if (arr[mid_index] === x) {
18.       return mid_index;
19.     }
20.    
21.     // Otherwise, if x is greater than elem at mid_index,
22.     // update left_index to be 1 above mid_index
23.     else if (arr[mid_index] < x) {
24.       left_index = mid_index + 1;
25.     }
26.    
27.  // Otherwise, if x is less than elem at mid_index,
28.     // update right_index to be 1 below mid_index
29.     else {
30.       right_index = mid_index - 1;
31.     }
32.   }
33.   // If x is not found, return -1
34.   return -1;
35. };
36.  
37. const myList = [2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12];
38. const result = binarySearch(myList, 6); // 4
39. console.log(result);