关于javascript的一个小问题，请问有人看出啥问题吗？

function binarySearch(){
    var arr = [0,1,2,3];
    var res = actbinarySearch(0,3,2,arr);
    document.write("<br/>return is "+ res);
}
function actbinarySearch(left,right,val,arr){ 
    
    if(left > right){
        document.write("do not find");
        return -1;
    }
    var midIndex = Math.floor((left+right)/2);
    var midVal = arr[midIndex];
    if(val < midVal){
        actbinarySearch(left, midIndex-1,val,arr);
    }else if(val > midVal){
        actbinarySearch(midIndex+1, right, val, arr);
    }else{
        document.write("find it "+midIndex);
        return midIndex;
    }
}