var a=[0,1,2,3,4,5,6,7,8]
    function Search(arr,target){
        var left;
        var right;
        var NotFound=-1;
        left=1;  //初始化左边界
     right=arr.length;   //初始化右边界
        while(left<=right){
            var mid=(left+right)/2;  //计算中间元素坐标
            if(target<arr[mid]){
                right=mid-1;         //当目标值小于中间值时，调整右边界
            }
            else if(target>arr[mid]){
                left=mid+1;          //当目标值大于中间值时，调整左边界
            }
            else{
                console.log(mid) ;   //找到 返回坐标
            }
        }
        return NotFound;    //没有找到
    }

Search(a,7)