 Implémenter un algorithme de recherche binaire.
 arr : [1, 2, 4, 6, 8, 10, 11, 15], x : 8
let start = 0 \nlet end = arr.length -1\nwhile (start <= end) {\n let mid = Math.floor((start + end)/2)\n if (arr[mid] == x ) {\n return mid \n }\n else if (arr[mid] < x) {\n start = mid + 1\n }\n else {\n end = mid - 1\n }\n}\ nretour -1