1. var arr = [12,13,14,15,17,19, 23,34,45,56,67,78,89,90]
    3. function midFind(arr, target){
    4.   var left = 0, right = arr.length -1
    6.   while(left < right){
    7.       var mid = Math.floor((right-left) / 2)
    8.     if(arr[mid] === target){
    9.       return mid
    10.     } else if(arr[mid] < target ){
    11.       left = mid + 1;
    12.     } else {
    13.       right = mid - 1
    14.     }
    16.   }
    17.   return mid
    18. }
    20. console.log(midFind(arr, 45))