二分法 binary_search

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