参考答案

参考回答：

function binarySearch(target,arr,start,end) {
var start   = start || 0;
var end     = end || arr.length-1;
var mid = parseInt(start+(end-start)/2);
if(target==arr[mid]){
return mid;
}else if(target>arr[mid]){
return binarySearch(target,arr,mid+1,end);
}else{
return binarySearch(target,arr,start,mid-1);
}
return -1;