给一个数，去一个已经排好序的数组中寻找这个数的位置（通过快速查找，二分查找）？

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;